The document, which names Sir Peter Hayman as the subject of a briefing compiled for then-prime minister Margaret Thatcher, is now available in the National Archives.

Sir Peter, who died in 1992, was High Commissioner to Canada and was worked for MI6.

The file is titled “Sir Peter Hayman: allegations against former public official of unnatural sexual proclivities; security aspects”.

The file bears the codename PREM 19/588, the prefix of which indicates it was prepared for the Prime Minister.

Sir Peter Hayman was branded a paedophile in 1983 by Conservative MP Geoffrey Dickens, who was speaking in parliament and was therefore protected from legal reprisals under privilege.

Geoffrey Dickens, who branded Hayman a paedophile in 1983 (Getty)
The file is dated October 1980 – March 1981 – years before the allegations by Mr Dickens were made public.

The document’s existence was revealed by Sky News earlier this year. Sir Peter’s name was previously redacted.

A Cabinet Office spokesman said: “This file was originally kept closed as it contained information from the security services and advice from the law officers. We have reviewed that decision and have now released the file into the National Archives.”

In November last year an alleged victim of abuse picked out a photo of Sir Peter Hayman and named him as his abuser, the Sunday People newspaper reports.

The abuse survivor, now in his 40s, told the Exaro news agency at the time: “He used to like to kiss and to touch, liked me to do that to him.

"But it would always culminate in me being raped. That happened all the time.”

It has been long known that Sir Peter was questioned by police after he left a package of paedophile material on a bus.

Officers found a large collection of similar material at the diplomat's flat in West London, but he was never prosecuted.

The information is likely to be of interest to the Government's inquiry into child sexual abuse by establishment figures.

Police are also investigating allegations of sexual attacks as Dolphin Square, as well as allegations surrounding alleged abuse at the Elm Guest House in South London.