The former Secretary of State for War John Profumo, who had an affair with Christine Keeler Reuters

Former Conservative minister John Profumo, who was forced to resign over an infamous sex scandal in the 1960s, previously had a long-running relationship with a Nazi spy, according to newly released MI5 files.

The glamorous German-born model and spy Gisela Winegard may have tried to blackmail Profumo, it has been revealed. According to The Guardian, Winegard and Profumo met in Oxford in 1936 when he was an undergraduate and the two kept in contact for at least 20 years.

Winegard ran a Nazi secret information service in occupied Paris and had a child with a high-ranking German officer. She was jailed for espionage when Paris was liberated in 1944.

During the height of Profumo's 1963 sex scandal, MI6 officer Cyril Mackay sent MI5 chief Arthur Martin a letter and files detailing the disgraced Tory minister's connection to Gisela Winegard (née Klein), the Guardian reported.

Profumo, then secretary of state, was forced to resign after he misled the House of Commons about his affair with Christine Keeler, who was also mistress to Soviet defence attache, Yevgeny Ivanov.

The newly declassified MI5 files include claims made by Winegard's American husband Edward Winegard in 1950, according to The Mirror. Edward claimed the couple separated because of her "endearing letters from John Profumo...written on House of Commons notepaper".

The Gisela and Edward, who were reunited by 1951, had an application for a UK visa rejected. MI6's letter to MI5 revealed authorities believed the couple had "recently engaged in blackmail activities and now think it is possible their intended visit to the UK may be connected with this".

Profumo was listed as a reference in the couple's visa application for a six-week visit.

A memo shows Profumo admitted in 1941 to meeting Winegard in the 1930s "and got to know her well". The memo continues: "[Tory MP from 1919 to 1945] Lady Astor is alleged to have expressed the opinion that she was a spy."

Security services history Christopher Andrew told The Guardian that Profumo may have been unaware of Winegard's involvement in Nazi intelligence.

Following the 1963 scandal, Profumo left politics to do charity work. He died in 2006 aged 91.