Tory grandee Ken Clarke warns euro exit is 'inevitable' as Greece's supporters rally in London

Ken Clarke says Britain must prepare itself for the economic shocks a Greek euro exit would cause

In a parliamentary career dating back to 1970, Mr Clarke served as Chancellor, Home Secretary, Education Secretary, Health Secretary and Justice Secretary (Getty)

A Greek euro exit is inevitable and Britain must insulate itself from the economic shocks it would cause, Ken Clarke has said.

The Conservative former chancellor issued his warning as UK-based supporters of the Greek government held a rally in London’s Trafalgar Square.

Talks are continuing between the country's new anti-austerity government and other EU member states about the conditions under which it should continue to pay interest on its sovereign debt and whether some of it should be forgiven.

Speaking on the BBC's Sunday Politics programme Mr Clarke said that there would be “knock-on effects” from a Greek euro exit.

“Just judging from the public statements of these latter-day Trotskyites who appear to have won the election in Greece, I can't see how that can be reconciled,” he argued.

“I hope a very great deal of work is going on to minimise the impact on financial markets, on the United Kingdom - because it affects us just as much anybody else in the western world - to make sure that any knock-on effects of from their exit are minimised, and knock-on effects on the Greek people, who are going to suffer more ... are also minimised as well.”

Mr Clarke is one of the most pro-European members of the Conservative party and sat on the Coalition government's front bench until last year.

As he spoke, thousands of people gathered in central London to show their support for Greece's leftist government.

The Let Greece Breathe protest, organised by the Greece Solidarity Campaign, was part of a wave of rallies in cities across Europe this weekend.

Speakers at the event included Labour MP Jeremy Corbyn and Billy Hayes, general secretary of the Communication Workers Union.

The comedian Russell Brand was also spotted in the crowd of the event, showing his support.