Image copyright PA

An MI5 letter warning of the risk of "political embarrassment" from child sexual abuse claims has been found.

A 1986 note - by then head of MI5, Sir Anthony Duff - followed warnings an MP had a "penchant for small boys".

The newly uncovered material, found in a search by the Cabinet Office, was not disclosed to a 2014 Home Office review.

Its author, the NSPCC's Peter Wanless, said the new documents showed the risk to children was "not considered at all" but did not alter his findings.

The papers have come to light months after the conclusion of an official review into whether allegations of child abuse were covered up by the Home Office in the 1980s.

The review - written by Mr Wanless and Richard Whittam QC and published in November - examined how the Home Office dealt with files alleging child abuse between 1979 and 1999.

It concluded that there was no evidence of records being deliberately removed or destroyed.

Historical child abuse: The key investigations

The inquiries and what happens next

But in a supplement to that review, Mr Wanless said the discovery of the new material by the Cabinet Office was "unhelpful" for public confidence.

Police are also examining the newly emerged material.

Many of the new files found were in a set of previously uncatalogued records called "Cabinet Secretary miscellaneous papers".

It included documents about three MPs - former home secretary Leon Brittan, ex-MP for Chester Sir Peter Morrison and former Wokingham MP Sir William van Straubenzee - although the contents of those papers is not known.

Former diplomat Sir Peter Hayman was also mentioned in the documents.

Image copyright NSPCC Image caption Peter Wanless said the emergence of the new material was "unhelpful" for public confidence

The MI5 letter, from Sir Antony Duff to the then Cabinet Secretary Sir Robert Armstrong, followed an inquiry into an MP alleged to have a "penchant for small boys".

The letter concluded that the MP's denial had been accepted and Sir Anthony wrote that "the risk of political embarrassment to the government is rather greater than the security danger".

Other newly disclosed documents make reference to the Kincora boys' home in Northern Ireland, which was at the centre of a child abuse scandal between the 1950s and the 1980s.

A 'misplaced priority'

Mr Wanless and Mr Whittam said references "across the papers" had reinforced the findings of their review, that allegations of child sex abuse were given "considerably less serious consideration than would be expected today".

Speaking to BBC Radio 4's Today programme, Mr Wanless said the discovery of the new documents was "not necessarily" evidence of a cover-up.

But he said the MI5 note was a "vivid example" of a "misplaced priority" that ran right through to "the highest levels of government".

"People simply weren't thinking about crimes against children and the consequences of those crimes, relative to other considerations such as national security and the reputation of departments and individuals," he added.