Whitehall must be more open and routinely publish information that does not need to stay secret, Richard Thomas said in his last speech as Information Commissioner.

Thomas, who is stepping down at the end of June, said the recent MP expenses saga, where details were leaked to the Daily Telegraph following a court ruling that they must be disclosed, has "cemented" the importance of the Freedom of Information (FoI) Act.

Public organisations should identify all information which genuinely cannot be made public and then release the rest - without waiting for FoI requests – according to Thomas, who called for a culture of "routine, proactive and substantially increased openness".

His speech comes a day after proposals to keep cabinet papers exempt from FoI laws for 20 years were announced.

"The Freedom of Information Act has been seen as a somewhat fragile flower for most of its lifetime. It has now come of age and moved centre stage – a permanent fixture and a core part of the fabric of public life."

"The public has a right to know what is done in their name and with their money," said Thomas, adding the public should be "treated like grown-ups".

Thomas also called for more resources: "Open government is good government, but it has to be properly paid for. Last year we closed 17 per cent more cases, but – reflecting the growing popularity of FoI – we received 15 per cent more complaints. My office is flat out, but too many cases still have to wait to get started. If the law is to be extended, that must be accompanied by adequate and secure funding."