The Information Commissioner will tomorrow demolish one of the main arguments being used by Government to introduce restrictions on people’s right to know about the State.

Richard Thomas, who will be appearing before MPs on the Constitutional Affairs Committee, is expected to say that public bodies already have wide-ranging powers to ignore requests that are designed to waste civil servants’ time.

The Government believes that laws introduced in 2005 requiring much greater disclosure of information from the public sector place an unfair burden on civil servants.

However campaigners say that the proposed restrictions are unnecessary and designed to save the Government from embarrassment after a series of damaging disclosures.

Under the changes, the public would no longer have the right to know who the Prime Minister is entertaining at Chequers, the extent of crimes committed by foreign diplomats and regional variations in the performance of the Crown Prosecution Service.

The changes are expected to lead to an extra 17,000 Freedom of Information (FoI) requests a year being turned down on cost grounds irrespective of the public interest, and will save £5.7 million, according to Lord Falconer of Thoroton, the Lord Chancellor.

Mr Thomas is expected to say that Government already has powers to refuse “vexatious” or malicious requests. His office, which acts as an appeals court for FoI requests, has strongly backed organisations that have used those powers in the past.

Mr Thomas has already given evidence to another Commons committee saying that only 6 per cent of public bodies had said that such requests were a problem.

A recent analysis found that applications for information were taking so long because ministers insist on a personal role in one in five requests to central government. This was never intended when the legislation was drafted, with requests involving ministers taking five hours more work than the average request and costing almost twice as much.

Under the proposals, opposition politicians, campaign groups and journalists will have to ration requests to public bodies or risk their inquiries being automatically rejected. Organisations such as The Times would be limited to two questions to a Whitehall department every 60 days.

In addition, requests for sensitive and controversial information will be more likely to be refused because they take up too much government time. Government departments can refuse requests if the cost of searching is more than £600. Lord Falconer is changing the rules so that would include “reading, consideration and consultation time”.

The changes have been widely condemned by MPs, members of the public and a coalition of almost all national newspaper editors; 1,609 members of the public signed a petition on the Downing Street website to “reject the restrictions” while 101 MPs have signed a early day motion calling on the Government not to proceed.

The Freedom of Information Act has been enthusiastically embraced by the public, with 121,000 requests a year, costing £35.5 million. The Government has estimated that the changes will result in a 19 per cent drop in requests.

Lord Falconer said that a small minority of requests, mainly from the media, had wasted civil servants’ time in order to feed the “wilder fevers of journalistic wish-lists”. One example he has cited was for a request for spending on lavatory paper. But critics point out that this information is already collated by government for the Sustainable Development Commission.

The Government claims that the changes are about not placing a burden on the time of public servants “who often had better things to do”.

But Graham Smith, Mr Thomas’s deputy, said after a recent ruling that public bodies already have powers to ignore malicious requests. “Rights to access official information should be exercised responsibly and the Act recognises that there are limits to compliance beyond which public authorities are not obliged to go.”

The Constitutional Affairs Committee is holding a one-off session tomorrow to examine the proposals. Alan Beith, the committee chairman, said: “We are extremely concerned that the Government might go ahead with these changes, which are very widely opposed.”

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