MI5 failed to prove its belief that poet WH Auden was involved in the defection of two of the "Cambridge spies", official documents show.
WH Auden's centenary is being celebrated this year
Guy Burgess and Donald Maclean fled the UK on 25 May 1951 after they had been exposed as passing valuable intelligence to the Soviet Union.
Newspaper reports and sources said Burgess had tried to contact his friend Auden in London a day earlier.
MI5 could not prove involvement as Auden holed himself up in Italy.
Burgess and Maclean defected to the Soviet Union three days before a planned interrogation by MI5, after being tipped off by US-based fellow Cambridge spy Kim Philby.
The Cambridge spies were all recruited as students at the city's university before securing sensitive government posts, from which they passed valuable intelligence to the Soviet Union.
Auden and Burgess had also met at Cambridge University.
Auden, who was married to Erika Mann - daughter of German novelist Thomas Mann - had been watched for years with a number of possible Communist connections being established, the documents released by the National Archives at Kew, west London, show.
He was described in a document from 1938 as "an intellectual communist of a highly-idealistic and literary brand".
WH AUDEN - THE POET
Born in York on 21 Feb 1907
Regarded as one of great 20th century writers
Published about 400 poems
1935 marriage to German Erika Mann was one of convenience that gave her UK passport
Move to US in Jan 1939, ahead of WW2, seen as a betrayal by some
Became naturalized citizen of US in 1946
Work enjoyed revival when Funeral Blues used in 1994 film Four Weddings and a Funeral
MI5 was first alerted to the Burgess/Auden connection when the Reuters news agency reported a conversation it had with the poet's childhood friend Stephen Spender.
Auden - whose centenary is being celebrated this year - had been staying at fellow poet Spender's house in St John's Wood, London.
"Reuters learned from Stephen Spender that Burgess had telephoned him on 24 May," it was noted on 11 June.
Two days later, the Daily Express reported from the Italian Island of Ischia, where Burgess was by now staying in his holiday home.
Interviewed by the paper, Auden admitted a call had been made to Spender's house on 24 May.
"I was out and Spender forgot to pass on the message," he told the paper.
"In fact, I did not know about the phone call until this week."
The Express article prompted the FBI to conclude "Auden may have considerable information of interest concerning Burgess".
Burgess had previously worked at the British Embassy in Washington.
MI5 noted "the Americans, of course, must take care not to base their enquiries on what has been said in the Daily Express".
Guy Burgess defected to the Soviet Union in May 1951
The documents say that, on 14 June, an unnamed source had spoken to Spender and his wife who "now remember definitely that Burgess telephoned twice between 20 May and 24 May - most anxious to get in touch with Auden".
When they had passed the message on to Auden, he had said Burgess "must be drunk", the source said.
But when the source spoke to Auden, he had "categorically denied having been given a message by Spender".
A note reads: "Our conclusions must be that either Auden or Spender is deliberately prevaricating."
A further minute from the source suggests it was, indeed, Auden who was deliberately prevaricating.
The source said that - on a subsequent meeting - Auden, who "had been drinking heavily", had "reluctantly admitted Spender was probably right in saying he had told Auden of Burgess's telephone calls".
The source "felt it likely that Auden was lying" previously.
A suggestion that Auden's old friend Burgess was also fond of a drink came in an interview with Auden's wife who had not joined her husband in Italy.
Mrs Auden had "no clear recollection of Guy Burgess", an agent wrote.
"She believed she met Burgess at parties in London but said she 'never recalled seeing him in a sober state'."
Despite his apparent about-turn, when interviewed by Italian police at the end of June Auden went back to his original story that Spender had not mentioned the call.
And so without solid evidence that Auden had anything to do with the disappearance of Burgess, the investigation ended.
The file ends with the summary: "These reports were investigated and, while there's no doubt that Auden and Burgess were acquainted, it proved impossible to substantiate the reports that they had recently been in touch."
Other files, also released on Friday, show that, in an interview on 12 June 1951, acquaintance Peter Pollock revealed Burgess's "greatest friend was Anthony Blunt".
That revelation is significant in light of the 1964 naming of Blunt as the fourth member of the Cambridge spy ring.