The concerns emerged after a number of experts unexpectedly resigned from their positions at the Cambridge Intelligence Seminar (CIS), an academic forum on the Western spy world.

The men - former MI6 chief Sir Richard Dearlove, Stefan Halper, a former policy adviser at the White House, and historian Peter Martland - are said to have left amid concerns that the Kremlin is behind a newly-established intelligence journal, which provides funding to the group.

Mr Halper told earlier reports that his decision to step down was due to "unacceptable Russian influence" on the group.

Last night, a former KGB spy chief said it is entirely possible the experts’ alleged fears are true.

The CIS was set up by official MI5 historian Professor Christopher Andrew. Seminars, which take place on Fridays at the university's Corpus Christi college, are advertised on the university website, with previous attendees including Mike Flynn, Donald Trump’s choice as new national security adviser for the US, and Dr Paul Martin, the ex-director of parliamentary security.