John Bercow has been accused of covering up the scale of alcohol problems in the Houses of Parliament.
The House of Commons Speaker used a controversial loophole in the Freedom of Information Act to withold information believed to raise concerns about the extent of drinking problems in Westminster's subsidised bars.
Taxpayers subsidise the sale of alcohol in around a dozen bars on the Parliamentary estate to the tune of £4m a year.
It means MPs, staff and other passholders can enjoy a pint of beer for as little as £2.90.
The extent of Westminster's drinking problem has been highlighted by a number of high profile incidents over the last few years.
Former Labour MP Eric Joyce was convicted of assaulting a fellow politician during a brawl in the MPs' bar in 2012, while former MP Mark Reckless apologised for missing a vote on the Budget in 2010 because he was too drunk.
Charles Kennedy's death last summer again put Westminster's drinking culture under the spotlight after a post-mortem found that his death was caused by his long battle with alcoholism.
The Alcohol Concern charity has urged Parliament to remove its taxpayer-funded subsidies in response to concerns over alcohol problems, while House of Commons authorities are believed to have conducted work to address the growing concerns.
But a Freedom of Information request by the Press Association asking the Commons authorities to disclose evidence or reports produced by its Safety, Health and Wellbeing Service relating to alcohol consumption in Parliament was rejected on the grounds that doing so would breach confidentiality.
The response from the Commons admitted it held "correspondence and reports to the Management Board" but said: "The Speaker of the House of Commons has formed the reasonable opinion, under the above sections of the Act, that disclosure of this information would inhibit the free and frank provision of advice and the free and frank exchange of views for the purposes of deliberation."
It added that Mr Bercow believed the publication of correspondence would "prejudice the effective conduct of public affairs".
The only information disclosed was that 18 appointments had been made to the Health and Wellbeing Service over "alcohol dependency" since 2012.
It comes as concerns grow over threats to Freeom of Information rules after the Government ordered a review of the Act and appointed a commission full of opponents of FOI to look into reforming the legislation.
There are fears that the Government could introduce measures to restrict the release of information, such as imposing charges on requests and giving ministers greater scope to block requests.
Maurice Frankel, director of the Campaign for Freedom of Information, accused Mr Bercow of using the loophole to protect the reputation of MPs.
"He is exploiting a loophole in the FOI Act which parliament itself has inserted to protect parliament from scrutiny," he said.
"On the face of it there is no reason why they should not reveal what their assessment of any alcohol problem in parliament is.
"It is a matter of public interest if any MP's or peer's conduct is being impaired.
"It is entirely reasonable for us to know whether they regard that as a problem, and what has been considered.
"It is extremely easy for parliament to avoid scrutiny under the FOI Act."