Advisers to Jeremy Corbyn were among communists investigated by MI5 for wanting to “destroy” democracy in the UK, the former head of the Security Service has claimed.

Dame Stella Rimington said that members of communist and Trotskyist organisations in the 1980s who attracted attention from MI5 are now “grown up and advising our would-be prime minister on how to prepare himself for power”.

She described their change in status as “quite an ironic turn of events”.

Dame Stella, 82, who worked for MI5 from 1969 until 1996, began investigating “subversion” as the head of the F2 section in the early 1980s, and handled files on members of the Communist Party of Great Britain and “various Trotskyist organisations”.

She claimed some of them were now members of Momentum, the left-wing organisation that helped rally support for his successful leadership bid.

Dame Stella told the Cheltenham Literature Festival: “I now see in Momentum some of the people we were looking at in the Trotskyist organisation of the 1980s, now grown up and advising our would-be prime minister Mr Corbyn on how to prepare himself for power.