Officials admitted there was a public interest in the Prime Minister's dealings with the News Corporation chairman and chief executive but said, on balance, that there was an overriding interest in keeping them secret so that Mr Blair could have "free and frank discussions" with people.
Critics, including some Labour MPs, have claimed that Mr Blair has given Mr Murdoch too much influence over government policy on issues such as cross-media ownership and Europe in an attempt to ensure that the mogul's newspapers, including The Sun and The Times, support the Labour Party.
A reader of The Independent, who tried to obtain details of "communications, correspondence and minutes" between Mr Blair, his advisers and Mr Murdoch since 1997, was first told that it would be too expensive to provide under the guidelines of the 2000 Act. When he narrowed down his request to cover a one-year period, he was told that the information would not be released anyway.
"I can confirm that the Prime Minister's Office holds information relevant to your request," Nikhil Rathi, a private secretary at Downing Street, told the reader. "We acknowledge that there are public interest factors in favour of disclosure of the information you have requested.
"However, on balance, we consider that the public interest factors in favour of non-disclosure outweigh those in favour of disclosure of the information you have requested."
The Number 10 official argued: "It is important for the effective conduct of public affairs that the Prime Minister is able to undertake free and frank discussions with a range of stakeholders. It is in the public interest that views are expressed as freely as possible."
In 1998, Mr Blair rang Romano Prodi, the Italian Prime Minister, to test political reaction to Mr Murdoch's takeover bid for the Mediaset broadcasting empire, owned by Silvio Berlusconi.
Pressure from Mr Murdoch is believed to have been a factor in Mr Blair promising a referendum on the proposed European Union constitution. It was scrapped after a "No" vote in the French and Dutch referendums killed off the constitution.
The man who requested the information has appealed against Number 10's ruling, which will fuel criticism of the way the Act is working. But Lord Falconer, the Constitutional Affairs Secretary, gave an upbeat assessment of its first year yesterday. He told a conference in Manchester that 87 per cent of the almost 40,000 requests for information received in 2005 were responded to within the time limit. "This is not good enough, obviously I want to see 100 per cent answered to time, but ... it does compare favourably with experience in many other countries," he said.
* The Freedom of Information Act was passed in 2000 but did not take effect until January 2005
* According to figures published yesterday, 36,013 requests were made during 2005 - 19,710 to government departments and 16,303 to other public bodies
* Of the 29,271 requests about which information was held, it was released fully in 19,192 cases, withheld fully in 5,401 cases, and partially withheld in 3,762 cases. 916 are still pending
* Whitehall departments granted 60 per cent of requests in full.
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