The ICO exists to empower you through information.

Sections 30 and 31 are closely related. Together they protect information which, if disclosed, would undermine the work of law enforcement agencies or increase the risk of the law being broken. However, there are important differences in how the exemptions apply and who can use them.

You cannot use section 31 to withhold information which would be covered by section 30 (even if you think the information would engage section 30, but the balance of the public interest would favour disclosure). However, whilst you cannot use both exemptions to withhold the same piece of information, you could use both in response to the same request as illustrated below.


Following an incident in which armed officers arrested a gunman, the police receive a request from a journalist seeking both the police’s protocols for deploying armed officers and details of the actual arrest.

The police would not hold the protocol for deploying armed officers for the purpose of any specific criminal investigation, so they could not rely on section 30 to withhold it. However, the information may be exempt under section 31, if the police could demonstrate that its disclosure could prejudice the prevention or detection of crime.

The information about the actual arrest would be exempt under section 30. Even the police concluded that the balance of the public interest favoured disclosure of this information, they could not rely on section 31.

You can also use both exemptions to refuse to confirm or deny whether you hold the same information, if you can demonstrate that:

  • the information (if you held it) would be held for the purposes of a criminal investigation; and
  • confirming or denying that you held that information could make it more difficult to enforce the law.

You can only claim section 30 if you have particular powers or duties to carry out investigations. Any public authority can claim section 31. The exemptions therefore complement each other, because you can use them to protect the same information held by different public authorities.


A village hall, owned and managed by the local parish council, is broken into. The clerk to the parish council provides a statement to the police in which they describe a number of suspects. The clerk also records the events and descriptions in a private report submitted to the parish council.

The police hold the statement for the purpose of a criminal investigation which they have a duty to conduct. Therefore, if they received a request they could rely on section 30 to withhold the statement.

The parish council does not have any duty to investigate the crime and so couldn’t rely on section 30. However, if disclosing the report could alert the suspects that evidence is held about the crime, the parish council could rely on section 31 to withhold the report. This is because disclosure could prejudice the apprehension of offenders.

Further information is available in our guidance on section 30 investigations and proceedings.