Crime Prevention and Investigation Defence

There is a specific statutory defence which may apply where an indecent image has been made for the purpose of preventing, detecting or investigating crime, or for the purposes of criminal proceedings.

However, this is a narrowly focused defence which should not be confused with a general right to download, collect or investigate indecent images of children.

At McMillans Solicitors, we occasionally advise individuals who initially believe they can rely upon this defence because they say they were investigating suspected offenders themselves. Some describe their activities as online vigilantism, while others explain that they were attempting to obtain evidence to pass to the police.

Although such explanations must be considered carefully, our experience is that the courts are understandably reluctant to accept a claim of this nature without convincing evidence.

This page explains the relevant law, the approach adopted by the Crown Prosecution Service (CPS), and why people who take it upon themselves to investigate suspected child abuse may face significant difficulties in establishing this defence.

What Is the Crime Prevention and Investigation Defence?

The relevant provision is section 1B(1)(a) of the Protection of Children Act 1978, introduced by section 46 of the Sexual Offences Act 2003.

It provides a defence to the offence of making an indecent photograph or pseudo-photograph of a child where the defendant proves that it was necessary to make the image for:

• The prevention of crime;
• The detection of crime;
• The investigation of crime; or
• The purposes of criminal proceedings.

The legislation extends to relevant activities connected with crime or criminal proceedings in any part of the world.

The full statutory provision can be found in section 1B of the Protection of Children Act 1978.

The crucial word is "necessary".

It is not enough to establish that an individual believed they were doing something worthwhile, or that the material might conceivably have been useful in exposing criminal activity.

The defendant must prove that the making of the image was necessary for one of the purposes specified in the legislation.

Does the Defence Apply to Making, Possessing or Distributing Indecent Images?

An important distinction is that the defence under section 1B applies specifically to a charge of making an indecent image under section 1(1)(a) of the Protection of Children Act 1978.

The legal definition of making an indecent image is wider than many people realise. It can include deliberately downloading an image from the internet or creating an electronic copy of an existing image.

Consequently, a person who deliberately downloads suspected indecent images for what they describe as an investigation may still be committing the offence of making those images unless the relevant legal requirements for a defence are satisfied.

Further information is available on our page dealing with making indecent images of children.

It is equally important to appreciate that section 1B does not provide an automatic defence to possession or distribution charges.

For possession under section 160 of the Criminal Justice Act 1988, or distribution and possession with a view to distribution under section 1 of the Protection of Children Act 1978, a different statutory defence of legitimate reason may be relevant.

Although the circumstances may overlap, the legal provisions are distinct and must be considered separately.

Who Is the Defence Intended to Protect?

The principal purpose of the legislation is to ensure that people who genuinely need to handle potentially illegal material in order to detect, investigate or prevent crime can do so without automatically exposing themselves to criminal liability.

Examples of situations in which the defence may potentially arise include:

• Police officers or other authorised investigators dealing with suspected indecent images as part of an investigation.
• Individuals working in internet safety or electronic communications who must handle material reported through established procedures.
• Appropriately authorised personnel identifying and reporting child sexual abuse material.
• People who unexpectedly discover suspected illegal material and, in genuinely necessary circumstances, make a limited copy for the purpose of reporting it to the appropriate authorities.

However, the existence of a professional role does not give someone unlimited permission to make or retain images. The particular activity must still be justified.

Importantly, the legislation does not expressly state that only police officers or authorised professionals can rely on section 1B(1)(a). An ordinary member of the public may, in principle, seek to establish the defence.

Nevertheless, the absence of a recognised investigative duty or other convincing explanation for why copying was necessary may make the defence considerably more difficult to establish.

What Does the CPS Say About This Defence?

The most useful guidance is contained in the Memorandum of Understanding between the Crown Prosecution Service and the National Police Chiefs' Council, updated in May 2026.

This document explains how the authorities approach situations where people have made copies of suspected indecent images while claiming to be acting for legitimate investigative or reporting purposes.

It identifies several important considerations.

1. Why Was the Image Made?

The authorities will examine how the person came across the material and why a copy was created.

A person responding to a report of suspected illegal material in the course of legitimate duties is in a different position from someone who deliberately searches the internet for indecent images without being asked or authorised to conduct an investigation.

2. Was the Material Reported to the Authorities?

The guidance places considerable importance on whether the images were reported to an appropriate authority and how quickly that happened.

Someone who immediately reports an unexpected discovery is in a very different position from someone who continues collecting material for weeks or months without informing the police.

A delay does not automatically defeat the defence, but it may require a convincing explanation.

3. Was the Handling and Storage Appropriate?

The police and CPS will consider how the material was stored, who had access to it and whether unnecessary copies were created.

Unnecessary personal storage, repeated downloading or sharing images with others may seriously undermine a claim that the activity was undertaken solely to prevent or investigate crime.

4. Was the Amount of Material Necessary?

The guidance makes clear that the number of copies made should be limited to what is necessary for the legitimate purpose.

For example, someone who unexpectedly encounters a suspected illegal image does not ordinarily need to search the remainder of the website, visit similar websites or download multiple additional images merely to establish that the original material should be reported.

The complete CPS guidance can be read here: CPS/NPCC Memorandum of Understanding, updated May 2026.

What If I Was Acting as an Online Vigilante?

This is an issue which sometimes arises when advising individuals accused of indecent image offences.

A person may explain that they were attempting to identify paedophiles, investigate websites distributing illegal material or gather evidence which they intended to pass to the police.

Some individuals describe themselves as acting as online vigilantes or believe that, because their ultimate objective was to expose criminal activity, downloading or retaining indecent images was justified.

Unfortunately, that explanation does not necessarily provide a legal defence.

The CPS/NPCC Memorandum of Understanding expressly discourages vigilantism. It states:

"Vigilantism is not merely unnecessary it is unhelpful"

The guidance goes on to make clear that individuals who take it upon themselves to seek out or investigate indecent images without a legitimate duty risk prosecution.

This is particularly significant because it directly addresses the justification sometimes put forward by self-appointed investigators.

The underlying concern is straightforward. An individual cannot simply appoint themselves as an investigator and assume that this authorises conduct which would otherwise constitute a serious criminal offence.

Police forces and recognised child protection organisations have established procedures for investigating and reporting child sexual abuse material. Private individuals who undertake similar activities without appropriate authority may create further copies of illegal images, interfere with investigations and contribute to the continued circulation of material depicting the abuse of children.

Why Is a Vigilante Defence So Difficult to Establish?

In our experience, an individual claiming to have acted as a vigilante can expect their explanation to be closely scrutinised.

There are several obvious questions which may arise.

• Why were you searching for indecent images in the first place? Was there a genuine reason to investigate particular material, or were you deliberately seeking out illegal content?
• Why was it necessary to download the images? Could the suspected criminal activity have been reported without creating copies?
• How many images were obtained? Was the activity restricted to what was necessary, or did it involve collecting substantial quantities?
• How long were the images retained? Were they promptly reported, or kept for an extended period?
• Did you actually contact the police or another appropriate authority? If not, why not?
• What evidence supports your explanation? Is there independent material demonstrating a genuine investigative purpose?

These are not separate statutory requirements, but they illustrate the factual issues that may be relevant to assessing whether the legal test of necessity is met.

The mere assertion that someone intended to expose offenders is unlikely to be particularly persuasive if the surrounding evidence suggests extensive downloading, repeated viewing, unnecessary storage or no genuine attempt to report the material.

Equally, an explanation should not be rejected solely because the person was not a police officer. Each case must be assessed according to the actual evidence and the statutory test.

The critical issue is whether making the relevant image was genuinely necessary for preventing, detecting or investigating crime, or for criminal proceedings.

What If I Downloaded Images Intending to Give Them to the Police?

This is a more specific variation of the same argument.

A person may acknowledge deliberately downloading illegal images but explain that the intention was to provide evidence to the police.

Such an explanation requires careful examination.

For example, there is a substantial difference between someone unexpectedly encountering suspected illegal material and making a limited copy because it was genuinely necessary to make an effective report, and someone deliberately seeking out indecent images and downloading substantial quantities for a proposed investigation of their own.

The fact that material was eventually handed to the police may be relevant, but it does not automatically establish that the original downloading was necessary.

Nor will a later decision to report material necessarily provide a defence for earlier conduct undertaken for a different purpose.

The evidence relating to the person's intentions, actions and the circumstances in which each image was made will need careful consideration.

Who Has to Prove the Defence?

Section 1B imposes a legal burden of proof on the defendant.

This means that it is not sufficient merely to raise the possibility that the images were made for the purpose of investigating crime and expect the prosecution to disprove that explanation.

The defendant must establish the statutory defence on the balance of probabilities. In other words, the court must be satisfied that the defence is more likely than not to be established.

This is a lower standard than the criminal standard of proof beyond reasonable doubt, but it still requires persuasive evidence.

In an appropriate case, contemporaneous communications, records of reports to the police, evidence of an authorised role and digital forensic material may all be relevant.

However, the burden of establishing this particular statutory defence should not be confused with the prosecution's general obligation to prove the elements of the alleged offence.

What If I Accidentally Came Across an Indecent Image?

An accidental encounter with suspected indecent material raises different legal considerations.

The law relating to making indecent images requires consideration of whether the act of making was deliberate and intentional, with knowledge that the image was, or was likely to be, an indecent image of a child.

The Court of Appeal considered these principles in R v Smith and Jayson [2003] 1 Cr App R 13.

Consequently, where an individual genuinely encounters an image without the necessary knowledge or intention, there may be an argument that the prosecution cannot establish the offence of making in the first place.

That issue is separate from the statutory crime prevention defence.

Furthermore, an initially accidental encounter does not automatically justify deliberately downloading, copying or storing additional material afterwards.

Other statutory defences may also require consideration depending upon the precise allegation. These include the lack of awareness defence, although that particular statutory defence applies to specified possession and distribution offences rather than the offence of making.

What Should I Do If I Discover Suspected Indecent Images Online?

If you unexpectedly come across suspected child sexual abuse material, the safest general approach is to report it promptly rather than attempting to conduct your own investigation.

The Internet Watch Foundation (IWF) operates a recognised reporting service for suspected online child sexual abuse images and videos.

You can make a report through the Internet Watch Foundation's reporting service.

You can also contact the police where appropriate. If a child is in immediate danger, contact the emergency services.

You should not deliberately search for further illegal material, download additional images, forward suspected indecent images to other people or attempt to identify suspected offenders through an unauthorised investigation.

Reporting a website or online location will not ordinarily require you to download the illegal images yourself.

If you have already downloaded or stored material and are concerned about potential criminal liability, obtain specialist legal advice before taking further steps. Do not forward suspected illegal images to a solicitor by email or messaging applications, and do not attempt to conceal, alter or destroy evidence.

Can the Defence Be Raised During a Police Investigation?

Yes. Where there is a proper factual basis, the circumstances surrounding the making of the images can be raised with the investigating officers and, where appropriate, the CPS.

However, the decision whether to advance a statutory defence of this nature should be made only after careful consideration of the evidence.

In particular, it may be important to examine:

• The circumstances in which the images were first discovered.
• Any searches undertaken before the images were downloaded.
• The dates, number and nature of the images.
• How and where the images were subsequently stored.
• Whether images were shared with other people.
• Any reports made to the police, IWF or another authority.
• Whether the forensic evidence is consistent with the explanation provided.

It may also be necessary to consider whether the prosecution can prove the offence of making at all, independently of the statutory defence.

Where an individual has been arrested or invited to attend a voluntary police interview, we would strongly recommend obtaining specialist advice before providing a detailed account of any supposed investigative activity.

Our website contains further information about police station representation in indecent image investigations.

Frequently Asked Questions

Can I download indecent images if I intend to report them to the police?

There is no general permission to download indecent images simply because you intend to report them. Section 1B may provide a defence if the defendant proves that making the particular image was necessary for one of the specified crime prevention, investigation or criminal proceedings purposes. Reporting suspected material does not ordinarily require downloading it.

Is being an online vigilante a defence to indecent image charges?

Not automatically. The CPS expressly discourages self-appointed investigations. A person claiming to have acted as a vigilante would still need to establish the relevant statutory defence, and deliberate searching, repeated downloading and unnecessary retention may seriously undermine the explanation.

Can an ordinary member of the public rely on section 1B?

Potentially. The wording of section 1B(1)(a) does not expressly limit the defence to police officers or other professionals. However, the person must prove that making the image was necessary for the relevant statutory purpose. A recognised investigative role and compliance with appropriate procedures may be important evidence.

What if I downloaded the images but never reported them?

A failure to report the material may significantly undermine the claim that downloading it was necessary to detect or investigate crime. The circumstances would need to be examined carefully, including any explanation for the absence of a report.

Does this defence also apply to distribution of indecent images?

Not directly. Section 1B applies to making offences under section 1(1)(a) of the Protection of Children Act 1978. Distribution allegations involve different statutory provisions and potentially different defences, including the defence of legitimate reason.

What if I genuinely believed I was helping to protect children?

A genuine belief may be relevant when assessing the circumstances, but it does not automatically establish the defence. The law requires the defendant to prove that making the image was necessary for the specified purpose.

Specialist Advice from McMillans Solicitors

At McMillans Solicitors, we specialise in defending individuals investigated and prosecuted for offences involving indecent images of children.

We understand that some clients genuinely believe their conduct was justified because they were attempting to expose criminal activity or report suspected offenders.

However, we also recognise the importance of providing realistic advice.

In our experience, the courts are unlikely to accept a general claim of vigilantism as sufficient justification for deliberately downloading or collecting indecent images.

The existence of the statutory defence does not mean that it will succeed in every case where someone claims to have acted with good intentions.

Our approach is to consider the relevant law, examine the available digital evidence and provide an honest assessment of whether there is a sustainable defence.

Where appropriate, this may involve instructing a digital forensic expert, making representations to the CPS or preparing the case for trial.

Where the evidence does not support the proposed defence, we will explain that clearly and advise on the available alternatives.

If you are under investigation for making indecent images and believe the crime prevention or investigation defence may apply to your circumstances, please contact us for confidential specialist advice.

Telephone McMillans Solicitors on 01992 566730 or contact us online.

You can also read about other statutory arguments on our Indecent Images Defences page.

Legislation and Official Guidance

• Protection of Children Act 1978, section 1B – Exception for criminal proceedings and investigations.
• Sexual Offences Act 2003, section 46 – Criminal proceedings and investigations.
• Crown Prosecution Service – Indecent and Prohibited Images of Children.
• CPS/NPCC Memorandum of Understanding concerning section 46 of the Sexual Offences Act 2003, updated May 2026.