Melita Norwood said her husband had disapproved of her spying

Mrs Norwood, from Bexleyheath, south London, worked for the KGB for 40 years and was believed to be the Soviet's longest serving spy in the UK.

In the 1940s she was a secretary with the Non Ferrous Metals Research Association and passed on vital secrets of Britain's nuclear weapons programme.

The story caused a sensation but the great grandmother was not prosecuted.

The then Home Secretary Jack Straw ruled that it would not be in the public interest to prosecute her.

He later told MPs that lessons had been learned from the case.

A lifelong communist, Mrs Norwood said in 1999 she had wanted to help Russia's "new system".

Mrs Norwood said her late husband Hilary was opposed to her actions.

Her secret role was revealed by a KGB archivist, Vasili Mitrokhin, who defected to the West in 1992.

Mrs Norwood's death on 2 June was announced by her biographer.