The campaign to protect the Freedom of Information Act has been given a major boost after it emerged that Britain's top civil servant is understood to be opposed to controversial changes to the legislation.

Sir Jeremy Heywood, the Cabinet Secretary, had said earlier this year that the FOI rules had a "chilling effect" on the operation of Government but is now believed to be against reforms that would make it easier for public bodies to withhold information from members of the public.

Instead he wants to make the current rules of the Act clearer, according to The Times. Sir Jeremy is understood to want to make the rules over when ministers can block the release of information clearer to ensure greater consistency across government.

Sir Jeremy's position on the Government's review of the FOI Act will play a crucial role considering his influence inside Whitehall.

His opposition to plans such as imposing charges on requests for information and giving ministers and officials greater scope to block requests is a further sign that the review will not recommend a major overhaul of the legislation.

The FOI Act was brought in by Tony Blair but he later admitted the legislation was his biggest regret.

The Government commission looking into whether the legislation should be changed has been tasked to consider the "public interest balance" between oppenness and the protection of "sensitive information".

Earlier this week the minister in charge of the FOI Act, Matthew Hancock, said he was opposed to toughening the rules on the public obtaining information.

A senior source told The Times that Mr Hancock would be "very happy" if the inquiry came back with no changes.

Last week Labour's deputy leader Tom Watson accused David Cameron of wanting to "govern from the gloom" with his plans to curb FOI rules and claimed the review of the transparency legislation was out of touch with the public’s desire for more openness, a “waste of taxpayers’ money” and “predestined” to recommend raising barriers to obtaining information.

He said Mr Cameron was trying to “reverse the transparency Labour introduced” and seeking to “turn off the lights, systematically making it harder for people to engage with policy making, retreating into a darker and more secretive place".

Labour would strengthen and extend the FOI Act, he said.

Mr Cameron was criticised for appointing a commission full of opponents of the Act to look into reforming the legislation, including former Home Secretary Jack Straw, a vocal critic of the law despite playing a role in introducing it.

A Government spokesman refused to comment on Sir Jeremy’s views. “The Government is committed to freedom of information, and the vast majority of requests are handled within the time limit," the spokesman said.