Communists who were once monitored by MI5 are now among Jeremy Corbyn's most senior advisers, the spy agency's former director-general said yesterday.

Dame Stella Rimington claimed that some of those close to the Labour leader had been watched over fears they could seek to subvert British democracy.

But she refused to name names, saying only that the advisers were 'familiar' and part of the far-Left Momentum grassroots group.

Dame Stella, who was the first female director-general of MI5, said: 'I see in Momentum some of the people who we were looking at in the Trotskyist organisations of the 1980s.

Communists who were once being spied on by MI5 are now among Jeremy Corbyn's (pictured right) most senior advisers, it has been claimed. The agency refused to name names, leaving people to wonder who it was referring to. Pictured with Mr Corbyn is advisor Seamus Milne

'They are now grown up and advising our would-be prime minister Mr Corbyn as to how to prepare himself for power.'

The former spy's first managerial job for the security service was as head of F2, which was a branch responsible for investigating trades unions and communist groups.

The 82-year-old told the Cheltenham Literature Festival yesterday: 'In those days, we were looking at the Communist Party of Great Britain and various Trotskyist organisations.

'Our job was to find out exactly who the members of the Communist Party of Great Britain were, and various subversive organisations that were identified as wishing to destroy the democratic system of this country.

'Now they advise Mr Corbyn, that's quite an ironic turn of events. Certainly, their names are familiar, shall we say that much.'

Dame Stella Rimmington's remarks have led to mass speculation about who she could have been referring to. One potential is Momentum founder Jon Lansman (pictured left) and Unite union's chief of staff Andrew Murrary (pictured right)

The remarks sparked speculation about which of the Labour leader's advisers Dame Stella had been referring to.

Labour MPs suggested possible candidates included Mr Corbyn's spin doctor Seumas Milne, Momentum founder Jon Lansman and the Unite union's chief of staff Andrew Murray, who worked for Labour's election campaign.

Last night a Momentum spokesman said: 'Nameless allegations harm our political debate, and we'd recommend Stella Rimington refrain from making them in the future.'

A spokesman for Jeremy Corbyn said: 'It is well-documented that a wide range of trade union and political activists, including future senior government ministers, were monitored in the 1980s by the security services.

'It would be a breach of the Official Secrets Act and her obligations as a former senior MI5 officer if Stella Rimington divulged privileged information.'

In May it was claimed Mr Corbyn was investigated by the security services over his links to the IRA at a time when he was campaigning for a united Ireland and supported convicted terrorists.

A source claimed his support for Irish republicans led security officials to look into his activities in the early 1990s.

This is not the first time Mr Corbyn's inner-circle has been mired in controversy over their Leftist views.

Shadow Chancellor John McDonnell described himself as a Marxist in 2013, and has admitted he wants to 'overthrow capitalism'. He said at the time: 'We've got to demand systemic change. Look, I'm straight, I'm honest with people: I'm a Marxist.

A Momentum spokesman slammed the allegations, saying: 'Nameless allegations harm our political debate, and we'd recommend Stella Rimington refrain from making them in the future.' Labour leader Mr Cobryn is pictured with adviser Seamus Milne (centre) and wife Laura Ilvarez (left)

Former director general of MI5 Dame Stella Rimington (pictured) made the allegations at Cheltenham Literature Festival

'This is a classic crisis of the economy – a classic capitalist crisis. I've been waiting for this for a generation.

'For Christ's sake don't waste it, you know; let's use this to explain to people this system based on greed and profit does not work.'

In 2015, Mr McDonnell read from Chairman Mao's Little Red Book – a book of quotes from the former Chinese communist leader Mao Zedong – in the House of Commons.

Dame Stella, who ran MI5 from 1992 to 1996, joined the security service in 1969. Her first post was to monitor communists in the South West.

She said: 'My first job when I joined the service, I was responsible for the Devon and Cornwall branch of the Communist Party of Great Britain.

'And my job was to know exactly who belonged to it, so should they ever apply for a job that gave them access to classified information, I would pop up and say, 'Ah, no.'

'That's why Trotskyists came into that area at the time.'