Evening Standard/London

In a boost to David Cameron less than a week before the Eastleigh by-election, Ukip MEP Marta Andreasen has quit her party and launched a scathing attack on leader Nigel Farage, dismissing the party’s chances of ever achieving real power.

She cited the Prime Minister’s speech pledging an in-out referendum on EU membership as a “game changer”.

The South East region MEP’s comments about Farage - in an open letter - come amid speculation Ukip could perform well in the crucial electoral test. Farage opted not to stand as a candidate himself - but was in the constituency again today trying to drum up support.

However, Andreasen said she did not believe the party could offer “real leadership”.

“Ukip has good people in it at grass roots that care about the future of the United Kingdom and our place in a re-negotiated relationship with Europe,” she wrote.

“Unfortunately, their party leader treats any views other than his own with contempt.

“Ukip is his plaything to mould and shape in any way he sees fit, regardless of the views of others, myself included.

“His actions, surrounding himself with an old boys club of like-minded sycophants, are dictatorial in sharp contrast to those of David Cameron, who has shown he can listen, adapt and do what is right for the country, not just for personal gain.”

Andreasen said Cameron’s keynote address on Britain’s relationship with the EU last month had convinced her the Conservatives were the “true referendum party”.

“I was also reassured by the financial deal that David Cameron got for Britain on the EU Budget,” she went on. “This is a matter very close to my heart and for which I have fought hard, and it is an important step for Britain in this battle.”

By contrast, the MEP said Farage’s decision not to stand as a candidate in Eastleigh after former Cabinet minister Chris Huhne resigned in disgrace showed Ukip was only a “pressure group”.

She warned Eastleigh voters that Ukip had no chance of victory, and supporting the party risked letting “the Lib Dems in via the back door”.

Conservative Party chairman Grant Shapps said: “I’m delighted to welcome Marta to the Conservative Party.

“She brings a wealth of experience - and a dedication to fight for what’s best for the British people in Europe. “

Farage said in a statement tonight: “Having left the OECD, the European Commission and Ukip in unpleasant circumstances the Conservative Party deserve what is coming to them. The woman is impossible.”

Labour faces coming a humiliating fourth place behind Ukip in next week’s Eastleigh by-election, senior party sources have admitted.

The “squeeze” will cast a cloud over leader Ed Miliband’s claim to lead a One Nation party by begging the question whether Labour is putting on votes in the South of England.

Officials are being candid about candidate John O’Farrell’s poor hopes partly because they want the media focus next week to be on the expected defeat for Conservative candidate Maria Hutchings.

If, as the polls and bookmakers strongly suggest, Hutchings is trounced by Liberal Democrat Mike Thornton in one of their 40 key target seats, there are likely to be Tory recriminations. A senior Labour source said: “We recognise that we are being squeezed. It is very hard work on the ground. This is a by-election with pretty unique dynamics. We will do our best, of course, but it is tough going.”

Last week, shadow justice secretary Sadiq Khan stressed the importance of winning, saying in an interview with the Standard: “We need a good turn-out in Eastleigh or it would give the impression there are no-go areas for Labour. We are in it to win.”

But it is the Tory v Lib-Dem battle that is seen as the most significant. A success in the by-election is one of five “hurdles” set by dissident Tory MPs for David Cameron this year if he is to silence leadership rumblings. Lib-Dem Chris Huhne won a 46.5% share of the vote in 2010.

His speeding points scandal seems to be having no effect, with some observers thinking the party might lift its share to 50%.