A spokeswoman for the Cabinet Office told the BBC: "The guidance will make clear that whether or not information is subject to the FOI Act depends on the nature of the information and not the format in which it is held.

"Government information held on private email accounts is within scope of the FOI Act."

This new guidance means that information contained in private emails and text messages between the prime minister and other ministers could be requested for publication.

The Cabinet Office said: "The question of how the FOI Act applies to information held on private email accounts is a complex area of the law. The Cabinet Office is preparing guidance on how this applies to Central Government Departments, and this will be published shortly."