DAVID Cameron and Conservative headquarters will tonight be bracing themselves for the expected embarrassment of losing the Clacton-on-Sea seat in a by-election, which is due to deliver Nigel Farage's Ukip its first MP.

But it is thought that the political earthquake will stop there and not reach Manchester as Labour, it is thought, will hold on to the other Westminster contest taking place today in Heywood & Middleton.

The late MP Jim Dobbin, whose death triggered the by-election, enjoyed a majority just under 6,000.

The view Ukip might fall short in Manchester seemed to be confirmed when Patrick O'Flynn, one of its MEPs, admitted that if the party's candidate John Bickley were to come at least "a good second", then the anti-EU party would have shown "across the north of England it is replacing the Tories and Lib Dems as the main opposition to Labour".

But the focus will be on the Essex coast, where the contest was sparked by the resignation in August of former Tory MP Douglas Carswell, who defected to Mr Farage's party.

The Eurosceptic politician represented Clacton since 2005 and at the last General Election won the seat with a very healthy majority of 12,068; 53 per cent of the vote.

Apart from the fact that Ukip has replaced the Liberal Democrats as the party of protest and done well in several by-elections since 2010, it is thought that Mr Carswell's local popularity will also help see him cross the finishing line first tomorrow morning.

When he switched parties, the former MP said only Ukip could "shake up that tiny little clique called Westminster".

Underlying Tory jitters, last week Mr Cameron joined party candidate Giles Watling on the stump, claiming that, despite the party holding the seat, the Tories were the "underdogs in this by-election" but, he stressed, defeat was not inevitable.

The result is due early tomorrow morning. The new MP for Clacton will take their seat next week.