The BBC's Jon Silverman: Government braced for further revelations from the archives

Archives smuggled to Britain by a KGB defector have revealed more information about former Scotland Yard policeman John Symonds, 63, who worked as a "Romeo" agent, seducing female diplomats.

Vasili Mitrokhin: More revelations to come?

Just 24 hours earlier the Home Secretary called for a full report from MI5 into 87-year-old great-grandmother Melita Norwood, exposed as the Soviet Union's longest-serving agent in Britain.

The inquiries are potentially embarrassing for the security service and the government, because both cases raise questions about how long intelligence officers have known about the pair's activities.

It has also emerged that Symonds was not unknown to the authorities.

Code-named Scot by his KGB paymasters, the former Detective Sergeant was allegedly recruited after fleeing Britain in 1969 under suspicion of corruption.

Former KGB officer Vasili Mitrokhin on why he defected from the Soviet Union (with translation)

He carried out undercover missions between 1972 and 1980.

He returned to Britain in 1980, gave himself up and served a two-year sentence on corruption charges. He now lives abroad again.

But in 1985 he gave a newspaper interview admitting his treachery, and alleging that the intelligence service had shown no interest in talking to him.

'More revelations to come'

Mr Symonds was revealed as a spy in the same documents which exposed great-grandmother Melita Norwood as one of the USSR's top Cold War agents.

Melita Norwood: Spied for nearly 40 years

The "Mitrokhin archive", smuggled to the UK by Russian dissident Vasili Mitrokhin in 1992, consists of several years' worth of KGB files.

The documents, which were handed over to the British authorities in 1992, are expected to lead to many more revelations in the coming weeks.

But those made so far have raised questions about why the authorities have taken no action over the past seven years.

Tom King, former Conservative defence secretary, and now chairman of the parliamentary security and intelligence committee, is to launch an investigation into the matter.

He suggested that no action may have been taken because there had been much more information in the files to investigate.

Report ordered from MI5

Liberal Democrat Foreign Affairs spokesman Menzies Campbell: ''There must be an investigation''

Home Secretary Jack Straw has ordered a full MI5 report into the Norwood case.

Conservative MP Michael Howard, who was home secretary from 1993 to 1997, said he had been unaware of Mrs Norwood's existence.

The revelations came to light when a BBC team was researching the forthcoming documentary The Spying Game.

Mr Symonds told the BBC about his role as a "Romeo" agent : "I was taught how to be a better lover.

"Perhaps I wasn't a very good one before, and needed that instruction. But it was very pleasant.

"I was taught by two extremely beautiful girls. That was quite an interesting part."