The Spy Scandal: Espionage And The Law - The British traitors who got away

THE PROSECUTION of Melita Norwood is not a straightforward matter. There are others who leaked information to the Soviets and have not been prosecuted.

In 1996 the release of the American "Venona" files - deciphered Soviet messages from the Second World War and early Cold War - led to the unmasking of Theodore Hall, an American scientist working on the "Manhattan Project" to build the first atom bomb.

In 1996, Hall admitted that he passed information to the Soviet Union about the project. He has never been prosecuted and lives in retirement in Cambridge, England.

Anthony Blunt (1907-1983) was the "Fourth Man" of the Cambridge spy ring. He acted as talent-spotter, supplying the names of likely recruits to the KGB. He confessed to his role only when he was promised immunity from prosecution after the defection of Kim Philby in 1963. Blunt rose to become the Queen's adviser on art. But after he was exposed as a traitor in 1979 he was stripped of his knighthood and academic honours.

KGB documents are not usually considered strong evidence to prosecute any suspected spy. Normally a confession or other collaboration is needed. Mrs Norwood was never approached by MI5 or the Special Branch over her spying. MI5 only seems to have considered prosecution earlier this year when officers learnt that she was to be named in Professor Christopher Andrew's book.

The Attorney General would have to consider carefully all the aspects of the case. Where the suspect is elderly, the events long ago, and there is no collaboration it may be deemed "not in the public interest" to continue. It would be a careful political and legal judgement. However, Mitrokhin's files have already resulted in successful prosecutions. Robert Lipka, who was an employee of the US's National Security Agency, was arrested by the FBI. He was recently prosecuted and jailed. It is understood he confessed to passing secrets to the Soviet Union in the 1960s.