Boris Johnson today promised to fight UKIP 'on the beaches of Clacton' in the bitter fight to stop the Eurosceptic party securing its first seat in the Commons.

But the London Mayor does not seem to have gone to the trouble of learning the name of the Tory candidate - former sitcom actor Giles Watling - who has been tasked with stopping the UKIP bandwagon in its tracks.

Quizzed on the radio about the Conservatives' chances in this week's by-election, Mr Johnson could only venture that the candidate was a 'superb man... Stirling? Girling? Something like that.'

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London Mayor Boris Johnson vowed to take on UKIP in Clacton, but then failed to name the Tory candidate in this week's by-election

Thursday's by-election was triggered by the shock defection of Douglas Carswell to UKIP, and polls suggest the former Tory MP will easily hold the seat.

It would be the first time UKIP has secured an elected seat in the Commons, with leader Nigel Farage hoping to use it as a springboard to more seats in the run-up to the 2015 general election.

Promising to 'fight them on the beaches of Clacton', Mr Johnson played down the impact of a UKIP win, which would see the party secure its first elected MP.

It would be a 'small earthquake in Chile', he said on LBC radio, adding: 'It won't necessarily change the price of fish.

'It will be, obviously, a disappointment if we don't win for the Conservatives, but we will fight again and there's always a general election to contest it again.'

But Mr Johnson was left struggling when presenter Nick Ferrari asked who the Tory candidate was.

'We've got a fantastic guy called ... superb man ... Stirling, Girling, something like that,' he said.

He could not even complete Mr Watling's name when prompted that he was called Giles and he had been in the 1980s sitcom Bread.

The mayor, who is set to return to Westminster at the general election, warned that votes for UKIP in May 2015 could result in a Labour government.

'No matter how strong UKIP is performing in some parts of the country, there is absolutely no way on earth they are going to get more than one seat or something like that at the general election,' he said.

'Indeed, I think it quite likely at the general election that they will be wiped out, so that any gains they make in the current crop of by-elections - and I suppose it is conceivable they might win something - they will lose.

'All they can do is take votes away from the only party, which is the Conservative Party, who are actually going to deliver a referendum.'

Home Secretary Theresa May campaigned in Clacton today with Tory candidate Giles Watling, a local councillor who used to be an actor in 1980s sitcom Bread

The by-election was triggered when Tory MP Douglas Carswell (pictured today), defected to UKIP in August

UKIP leader Nigel Farage hopes to secure his first elected MP in the Commons in Clacton

Surprisingly, Mr Johnson went on to say he agreed with Mr Farage on several issues, but stressed only the Tories could win the general election.

He added: 'The problem is you vote Farage, you get Miliband. That is the tragedy. In many ways there are things that I agree with that Nigel Farage says. He seems to have ... the right approach to many issues.'

Mr Johnson said a 'pretty big item of agreement' with Mr Farage was on the need for a referendum on European Union membership.

He added that Mr Farage is a 'low tax sort of guy and he is a small state sort of guy and that also appeals to me'.