Margaret Thatcher had a secret meeting with Rupert Murdoch at Chequers weeks before his 1981 purchase of the Times newspapers, newly released files show.
A note by her press secretary Bernard Ingham says the prime minister thanked Mr Murdoch for "keeping her posted".
But the contentious issue of whether to refer the bid to the Monopolies and Mergers Commission was not raised.
The official history of the Times had stated there was no direct contact between the pair at that stage.
The papers are being released by the Margaret Thatcher Archive Trust.
The note by Mr Ingham (who became Sir Bernard in 1990) refers to a lunch with Mr Murdoch at Chequers on 4 January 1981, "to be treated Commercial - In Confidence".
It details the News Group chairman's intention to buy the Times newspapers and its supplements from the Thomson family.
Other papers among the archive reveal a hidden rebellion among backbench MPs, Ronald Reagan's doodles, and Margaret Thatcher's letter to a girl whose parents were divorcing.
'Reduction in manning'
According to Sir Bernard, Mr Murdoch told Mrs Thatcher he wished to make the Times operation profitable by introducing new technology and "a 25% reduction in overall manning".
During the meeting, he also stressed "the inevitability of progressing gradually".
"Nor did he accept that printing outside London was an option; he was firmly of the opinion that the titles must be printed in London", wrote Sir Bernard.
The files show the key political question of whether Mr Murdoch's bid should be referred to the Monopolies and Mergers Commission (MMC) was not considered at the meeting.
At the time, Mr Murdoch already owned the Sun and News of the World newspapers.
The Fair Trading Act 1973 required that all significant newspaper takeovers be submitted to the MMC, unless the Secretary of State certified a paper was unprofitable and under threat of closure.
In the end, this clause enabled the purchase to go ahead without a referral because of major losses at the Times.
Redundancies had already been announced by the Thomsons, which owned the newspaper.
However, the Sunday Times had remained profitable during that period and was expected to return to financial health.
The takeover issue was first discussed in government at the cabinet economic strategy committee on 26 January 1981, chaired by Mrs Thatcher.
Recently-released minutes of the meeting show that the PM began by highlighting the exemption under the Fair Trading Act allowing Mr Murdoch's bid to avoid referral to the MMC.
Chris Collins, the only historian to have studied the papers closely having worked for Mrs Thatcher since 1992, told the BBC the meeting with Mr Murdoch at Chequers was clearly "fresh information".
"He's not setting out some great plan to absolutely transform the British newspaper industry. He's hinting at it, but he certainly doesn't go far in that direction."
Mr Collins said the meeting was "not really an attempt to do a political deal".
"His great asset, which he lays out before her, is that actually he's the only person who wants to keep the Times going... he's in a very strong position and he knows it."
'See you in New York'
Sir Bernard's note finally recalls how "the Prime Minister thanked Mr Murdoch for keeping her posted on his operations".
"She did no more than wish him well in his bid, noting the need for much improved arrangements in Fleet Street affecting manning and the introduction of new technology."
In a letter included in the archive, Mr Murdoch later wrote: "It was kind indeed of you to let me interrupt your weekend at Chequers 10 days ago and I greatly enjoyed seeing you again.
"The Times business is proceeding and the field has contracted down to only two or three of us. Thomsons will make up their mind in the next day or so.
"We hope to see you in New York on the 28 February."
Trouble in Wapping
Following his successful takeover of the Times newspapers, Mr Murdoch established the News International printing plant in Wapping, east London.
It was here in 1986 that violent protests broke out over working conditions and the dismissal of employees.
It became one of Britain's most bitter industrial disputes, lasting a year and effectively breaking the power wielded by print unions over the newspaper industry.
Along with the miners' strike of 1984-1985, the trouble in Wapping is often seen against a background of new legislation to curb the influence of the unions, brought in by Mrs Thatcher.
The revelation of the 1981 meeting between Mrs Thatcher and Mr Murdoch comes after recent evidence given to the Leveson Inquiry revealed an allegedly cosy relationship between the press and politicians in the UK.
The Leveson Inquiry was set up in July 2011 to examine relations between the press, politicians and police following the phone-hacking scandal at News International.
Mrs Thatcher's private papers are among a collection being made available to the public at the Churchill Archive Centre (CAC) in Cambridge and on the website of the Margaret Thatcher Foundation.
The meeting between Mrs Thatcher and Mr Murdoch was specifically denied in The History of The Times, Volume VII, Graham Stewart's book covering events at the newspaper between 1981 to 2002.
The publishers of the Times have not commented on the release of the files.