A top British diplomat was the focus of a secret government file about his "unnatural" sexual behaviour.

The file, which has just been released to the National Archives, names the late Sir Peter Hayman as the subject of the file prepared for then-Prime Minister Margaret Thatcher.

It has now been transferred to the archives in Kew, south west London, under the title "PREM 19/588 SECURITY. Sir Peter Hayman: allegations against former public official of unnatural sexual proclivities; security aspects".

Sir Peter died in 1992 but during his career worked as a diplomat including as High Commissioner to Canada. He also worked for intelligence service MI6.

He was named as an abuser of children by the MP Geoffrey Dickens in the 1980s and also had links to the controversial Paedophile Information Exchange (PIE).

The existence of the file in the National Archives catalogues was highlighted by Dr Chris Murphy, a lecturer at Salford University, who alerted Sky News.

Dr Murphy said he was pleased at the decision to release the file.

He told Sky News: "I'm surprised - albeit pleasantly so - to see a decision to withhold a file under Section 3(4) of the Public Records Act reversed like this.

"In my experience this is quite unusual and I think it has to make us wonder about the decision to withhold it in the first place."

The file has been retained on grounds of national security and held by officials at the Cabinet Office, the department responsible for the smooth running of government.

Following the Sky News report the matter was raised in the House Of Commons, where MPs called for it to be made public.

MP John Mann, who campaigns on the issue of child abuse, said: "All of these files that have been classified need to be opened up.

"This one is of great importance. There could well be some very significant information in it and it needs to be looked at."

Peter Wanless, chief executive of the NSPCC - who was commissioned last year by the Home Office to examine Government files that may be relevant to the abuse inquiries - told Sky News that to the best of his knowledge he did not see this specific file during his inquiries.

Tom Watson MP said on Friday: "Without Sky News revealing the existence of this document, it wouldn't have been made available for public scrutiny.

"What else was known about Hayman and his associates?"