Claims that a police investigation into a suspected paedophile ring was shut down after a member of the royal family and an MP were implicated emerged yesterday.

The allegations were made by an ex-policeman and the inquiry is said to have been closed by the Crown Prosecution Service for "national security reasons".

The former officer said he was informed of the alleged cover-up by a detective sergeant who was based at London's Marylebone Police station in the late 1980s.

"I was in a car with two other vice squad officers. They were discussing a madam who had provided a girl of about 15 to Oliver Reed," the ex-official said to the Sunday Mirror.

"The detective sergeant said he had just had a major child abuse investigation shut down by the CPS regarding a royal and an MP. He did not name names, but he said the CPS had said it was not in the public's interest because it 'could destabilise national security'."

Sir Allan Green, who served as the Director of Public Prosecutions between 1987 and 1992 said he was unaware of any paedophile investigations been dismissed for national security reasons.

Sex abuse witness appeal

The allegation comes hot on the heels of a fresh Metropolitan Police appeal this week which urged victims of child sex abuse to come forward.

"If anyone has been a victim of non-recent sexual abuse I want them to come forward," said Deputy Assistant Commissioner Steve Rodhouse, head of Crime and Operations at the Met.

"The point to make… is that we will go where the evidence takes us, without fear or favour," he added.

The Independent Police Complaints Commission (IPCC) is currently looking into allegations of Metropolitan Police corruption and is specifically investigating 14 cover-ups of child sex abuse by high profile figures.

"These allegations are of historic, high-level corruption of the most serious nature," said Sarah Green, deputy chairman of the IPCC.

"We will oversee the investigations and ensure that they meet the terms of reference that we will set. Allegations of this nature are of grave concern and I would like to reassure people of our absolute commitment to ensuring that the investigations are thorough and robust."