Secret love letter shows softer side of Cambridge spy ring’s alleged fifth man

Intimate correspondence between John Cairncross and Gloria Barraclough features in National Archives exhibition

It was a love letter written by one of the more important British spies of the cold war that made Tom Brass realise he had never fully known his mother.

The spy in question was John Cairncross, the alleged fifth man in the Cambridge spy ring, whose spycraft also helped the Soviets win the Battle of Kursk and turn the tide of the second world war.