David Cameron's four visits to Newark appear to have paid off according to a poll which indicates the Conservatives are on course to hold the constituency in Thursday's by-election.

Lord Ashcroft's poll puts the Tories on 42 per cent, 15 points ahead of second-placed Ukip on 27 per cent, with Labour trailing in third on 20 per cent.

The results show an upturn in support for the Conservatives compared to last week's Survation poll for the Sun which put the party on 36 per cent, with Ukip on 28 per cent and Labour at 27 per cent. Lord Ashcroft said the differences shown by the two surveys could be down to his counting of "shy voters" who refuse to say or claim not to know how they will vote in relation to how they voted in the last election, with more of these likely to be Tories. The Tory peer also released figures showing 70 per cent of voters planning to back Ukip's Roger Helmer in the by-election are doing so in a general protest to show they are unhappy with all the parties.