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Voters are starting to desert Ukip as the campaign hots up.

A poll in 10 Tory-held marginals showed Ukip support falling by up to 10 points.

It will be a new blow for leader Nigel Farage, pictured by a sign at a Grimsby quay warning: “Caution – slippery” before taking a trip with reality TV star Joey Essex.

The Lord Ashcroft poll showed the Tories holding on to five seats, losing four to Labour with a tie in the other.

He said: “The most notable change was a move towards the two main parties. UKIP’s share had fallen by 10 points in nine seats.”

He said Lib Dems going over to Labour could hurt the Tories.

“In two seats with a Labour lead the Tory vote was the same as in 2010.

Lib Dem switchers to Labour account for the new state of play.”

There was another boost for Labour in a seat on London’s outskirts - home to a series of marginals Ed Miliband needs to clinch if he is to form a majority government.

The poll found Labour had turned a three point Tory lead in Harrow East five months ago into a four-point Labour advantage.

Interviewers quizzed 10,006 adults by telephone in 10 constituencies between March 28 and April 4.