John Bercow has been accused of dodging scrutiny by suppressing reports detailing the scale of alcohol problems at parliament.
The Speaker has invoked a controversial loophole in the Freedom of Information (FOI) Act to withhold material thought to raise concerns about the extent of drinking in Westminster's subsidised bars.
The move, in response to a request by the Press Association, follows a series of incidents that highlighted the issue of alcohol at parliament.
There are around a dozen bars and restaurants on the estate serving politicians, staff and other passholders, and the taxpayer subsidy of some £4 million a year means a pint of beer costs as little as £2.90.
Former MP Eric Joyce was convicted of assaulting a fellow politician during a brawl in Strangers' Bar in 2012, while another ex-member, Mark Reckless, confessed to missing a late-night parliamentary vote in 2010 because he was too drunk.
Dr Sarah Wollaston, Totnes MP and now health select committee chairwoman, warned in 2011 that some of her colleagues were drinking "really quite heavily".
"Who would go to see a surgeon who had just drunk a bottle of wine at lunchtime? But we fully accept that MPs are perfectly capable of performing as MPs despite some of them drinking really quite heavily," she said.
Commons bar staff have previously been given extra training on how to refuse to serve drunk customers, and told to top up glasses less frequently at functions.
Alcohol Concern has urged parliament to remove subsidies from booze in its outlets.
The House authorities are believed to have conducted work to establish the extent of problems and consider ways they could be addressed.
The FOI request sought "any evidence or reports produced by the Safety, Health and Wellbeing Service regarding the provision and consumption of alcohol on the parliamentary estate, and related health effects".
The House authorities admitted it held "correspondence and reports to the Management Board", but cited Section 36 as grounds for keeping them secret.
"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," the response said.
"Further correspondence is withheld under 36(2)(c) because the Speaker of the House of Commons also considers that the disclosure of this correspondence would prejudice the effective conduct of public affairs.
"In the case of the House of Commons, Section 36 of the FOIA provides an absolute exemption and the public interest test does not apply."
The only information the House did disclose was that nine appointments were made with the Health and Wellbeing Service over "alcohol dependency" in September 2012, and none the following month.
The House of Commons is the only public body that can use the Section 36 exemption without demonstrating that the public interest is weighted against disclosure.
The Information Commissioner cannot even analyse the reasons for the Speaker's decision, as a certificate signed by him constitutes "conclusive proof" the exemption has been properly applied.
The same mechanism was deployed three years ago to avoid revealing details of Mr Bercow's tax bill for his grace-and-favour residence, which had been requested under FOI by the Press Association.
Maurice Frankel, director of the Campaign for Freedom of Information, said Mr Bercow appeared to be "avoiding scrutiny" to prevent damage to 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."