Peters & Peters

The importance of raising ‘all reasonable lines of inquiry’ early in criminal investigations

In August 2023, then Home Secretary Suella Braverman wrote to all senior policing officials in England and Wales, commending them for their “agreement to a national commitment to follow all reasonable lines of enquiry [sic] for all crime types”.

The letter, covering a wide range of topics, was clearly focussed on trying to encourage the public to have greater confidence that the police were pursuing “minor” crimes (e.g. shoplifting, anti-social behaviour). However, in a letter concerning reasonable lines of inquiry, one would have hoped to have seen consideration (or even mention) given to those under investigation. Instead, there was none.

What are reasonable lines of inquiry?

When investigating an individual (or company) for a criminal offence, investigators are under a statutory duty to “pursue all reasonable lines of inquiry, whether these point towards or away from the suspect. What is reasonable in each case will depend on the particular circumstances”.1

Investigators are also under a substantially broad duty to obtain “relevant material”. Relevant material is anything that “has some bearing on any offence under investigation or any person being investigated, or on the surrounding circumstances of the case, unless it is incapable of having any impact on the case”.2

Reasonable lines of inquiry can include (albeit not exhaustively):

– obtaining a copy of a complainant’s phone;
– obtaining CCTV footage;
– obtaining copies of records held by third parties, such as accounting records, tax returns, medical records, or therapy notes etc;
– obtaining draft copies of witness statements;
– the police speaking to other individuals with relevant information or knowledge; and
– material held by social media and tech companies, such as X, Meta, Google etc.

In 2022, the Attorney General (as a result of a number of high-profile cases collapsing due to disclosure issues) published guidelines on disclosure which states:


“The CPIA Code and these Guidelines make clear that the obligation on the investigator to pursue all reasonable lines of inquiry in relation to any offence under investigation, its surrounding circumstances or any person being investigated. This requires the investigator to pursue all lines of inquiry, whether they point towards or away from the suspect to, that may reveal relevant to the investigation or likely issues at trial. This obligation is the same in respect of material held by third parties within the UK.”


Passive or proactive – why engage with investigators?

Often suspects do not appreciate the significance of the duty that falls on investigators, and they will often see the police investigation as one sided, and lacking fairness and impartiality. It can, at times, feel like the police are “out to get you”. Similarly, many view the inarguable position that it is for the state to prove the guilt of a suspect, rather than for a suspect to prove their innocence, along with the right to silence, as reasons not to provide investigators with information.

However, raising issues that assist a suspect’s case, be it to prove that they have been wrongly identified, or to contextualise or clarify their actions to demonstrate that they have not committed a criminal offence, are particularly important when, prior to charge, the duties on investigators are both broad and clear.

Once a reasonable line of inquiry is raised and established, it is often the position that a suspect’s lawyers will have to deploy a proactive approach to ensure these lines of inquiry are pursued. This is important as investigators may not initially appreciate the significance of a line of inquiry, or understand why they need to follow a particular reasonable line of inquiry.

Investigators do not have to pursue “fanciful or inherently speculative searches”, but reasonableness can be established by demonstrating “an identifiable basis that justifies taking steps in this context”.3

Consequences of failing to follow reasonable lines of inquiry

A failure to follow lines of inquiry can be devastating on a decision to charge an individual. Often, when a case is charged, and concludes with the prosecution offering no evidence or discontinuing proceedings, it relates to the investigator’s failure to follow established reasonable lines of inquiry during the investigation stage.

Raising reasonable lines of inquiry from the outset can therefore be of great significance if a suspect is nevertheless charged with a criminal offence, as it enables a defendant to establish investigatory failings. This can include, and in our experience has included the failure to:

–  check the validity of documents, or eligibility for holding documents;
–  obtain expert evidence;
–  obtain third party material held as a result of other linked legal proceedings, be it by lawyers or courts and tribunals; and
–  fully and adequately analyse a complainant’s social media or mobile phone.

While there can be good reason for not wishing to engage with the authorities while under investigation, in appropriate cases, there can be very good reason for the lawyers to do so.

Often, engagement will decrease the risk of being charged with a criminal offence and can ensure that material that is needed to assist a suspect is obtained at the earliest opportunity (and importantly, not lost due to the passage of time).

Moreover, it can also reduce the length of time it takes to receive an outcome from the investigator, and if successful, enable suspects to return to their normal personal and professional lives, without the stress of a criminal investigation hanging over them..


1 Paragraph 3.5 of the CPIA Code of Practice issued under section 23(1) of the Criminal Procedure and Investigation Act 1996 (CPIA 1996).
2 Paragraph 2.1 of the CPIA Code of Practice issued under section 23(1) of the CPIA 1996.
3 Paragraph 70, R v Bater-James & Anor [2020] EWCA Crim 790.