Melita Norwood timeline

The spying career of Melita Norwood goes back more than 50 years:

1937 Melita Norwood gets a job as a secretary at the British Non-Ferrous Metals Research Association.

1945 She is cleared for access to sensitive documents despite security service concerns over her links to communist groups.

1949 Her access to secrets is blocked after further inquiries uncovered further worries about her sympathies.

1951 Her vetting clearance is revoked.

1962 Again, her vetting clearance is rejected.

1965 The security service received further information and concluded that Mrs Norwood had spied for the KGB in the 1940s. She was not interviewed, however, as intelligence officers wanted to hide how much they knew and to protect other investigations.

1992 Former KGB officer Vasili Mitrokhin defects and MI6 agent Richard Tomlinson brings back to the UK six trunks of archive information about Russian agents. Suspicions about Mrs Norwood are confirmed, but MI6 decides there is not enough evidence to prosecute.

It is again decided not to interview her in order to protect other investigations into more recent espionage. Ministers were not told about this decision.

1996 The then Conservative Government decides the Mitrokhin archive should be made public. Foreign Secretary Sir Malcolm Rifkind agrees to the papers being made available to Professor Christopher Andrew of Cambridge University.

1997 Current Home Secretary Jack Straw is first told about the Mitrokhin archive.

1998 In December, Mr Straw is informed for the first time heard about Melita Norwood's role and is told the Security Service was considering whether to prosecute.

1999, 22 April Mr Straw is told that the Attorney General had advised against prosecution as it would be "inappropriate".

1999, 29 June The Attorney General explains his decision in more detail, saying he believed that the "last opportunity" for any criminal investigation or prosecution had been in 1992 - and that therefore he had no decision to make.

1999, 31 August Mr Straw is told the Security Services were seeking advice on whether Mrs Norwood's alleged confession to the BBC could be used against her - if so, it could reverse the previous position on non-prosecution.

1999, 11 September Mrs Norwood is exposed as a spy.

1999, 29 December Solicitor-General Lord Williams of Mostyn announces that she will not be prosecuted.