Alan Beith has criticised a Cabinet Office instruction to staff to delete all emails after three months unless they are important.

The senior Liberal Democrat MP said all emails in government departments should be kept in case they become the subject of inquiries under freedom of information legislation.

Speaking on BBC Radio 4’s Today programme on Monday, Beith called on the information commissioner Richard Thomas to undertake an urgent review of the status of emails under the Freedom of Information Act.

The Cabinet Office’s instruction came just days before the implementation of the law on January 1, 2005.

The act grants citizens the right to see government documents except in limited cases where they might betray commercial confidences or harm national security.

The Cabinet Office said the timing was a coincidence, and that the measure was simply a matter of “good computer maintenance''.

Beith, who is also chairman of the Commons constitutional affairs committee, said the plan "could clearly lead to the removal of information which is absolutely crucial".

His committee has just completed a review of preparations for the implementation of the act, and would have had “pretty searching questions'' for the Cabinet Office if it had known of its plans, he said.

Emails have proved pivotal in recent inquiries, including Sir Alan Budd's review of David Blunkett's handling of a visa application and Lord Hutton's investigation of the circumstances of the death of government scientist David Kelly.

“Once the information is created, it should stay in the system and the freedom of information mechanism is there to enable people to get access to it if it is relevant to an inquiry,'' he said.

“The information commissioner needs to look at this aspect of the problem. He is there to protect the system.

“I think one of the first things he is going to have to do after January 1 – although he may have a few other problems on his plate – is to look at how the email regime can properly support the freedom of information regime.''

Beith added: “This is not supposed to be an inconvenient chore for departments. It is supposed to be a change of culture where it is recognised that the public is entitled to know all about how the government makes its decisions.''