A JUBILANT Nigel Farage has insisted Ukip could become a major force at Westminster after his party's second dramatic by-election victory, taking the seat of Rochester and Strood in Kent from the Tories.

Douglas Carswell, Ukip's first directly elected MP, predicted the party could now win dozens more seats and even suggested they might replace Labour as the main opposition.

David Cameron, who visited the constituency five times and famously pledged to "throw the kitchen sink" at the seat, vowed to win it back at the May General Election.

But, in the wake of the anti-EU party's win, the Prime Minister came under immediate pressure to toughen his immigration policy.

Hertfordshire MP and former Cabinet minister Peter Lilley called for an emergency brake on the number of migrant workers coming from the EU, declaring: "It would be absolutely right to have emergency measures."

His Tory colleague Andrew Bridgen urged Mr Cameron to counter Ukip's appeal by promising to put himself at the head of the campaign to leave the EU if he was unable to achieve a satisfactory re-negotiation of the terms of Britain's membership. "We need the Prime Minister to say that and that will take the legs from under Ukip," claimed the backbencher.

Attention is now turning to the Conservative leader's eagerly awaited keynote speech on Europe, due before Christmas.

Amid jubilant scenes, Tory defector Mark Reckless - who stood down in order to trigger the showdown with his former party - regained the Kent seat with a majority of 2,920; the previous Conservative one was almost 10,000. Turnout was just more than 50 per cent.

Within hours he was in the Commons being sworn in; Tory MPs looked on stony-faced.

Noting that Rochester was Ukip's 271st target seat, Mr Farage said the victory showed the party was now capable of winning anywhere in the country.

"We have beaten the governing party of the day in this sort of life-and-death struggle. It represents a huge, huge victory. I would be very surprised, given where we are, if there weren't more defections between now and the next General Election. They won't happen today, they won't happen tomorrow but over the course of the next few weeks people will be thinking and perhaps some of them saying to themselves, 'You know what, I have got a better chance of winning on a purple ticket than I have on a blue ticket'."

In response, Michael Gove, the Conservative Chief Whip, insisted he remained "100 per cent certain" there would be no more defections to Ukip, although William Hague, the Commons Leader, sounded less sure, saying: "I don't have a crystal ball about what every MP will do."

A number of prominent Tory Eurosceptics, including John Baron, Philip Davies and Stewart Jackson, came out to declare their allegiance to the Tory Party.

Among Conservative high command, there was some relief the final margin of defeat was narrower than many commentators had predicted.

The Liberal Democrats were also heavily punished by voters for effectively ignoring the contest; they polled just 349 votes, their worst ever result, representing less than one per cent.

Labour's share of the vote was almost halved to just 6,713, but their biggest blow was self-inflicted after London MP Emily Thornberry tweeted a picture of a home covered in England flags and with a white van parked outside. The resident, Dan Ware, branded her a snob.

The Shadow Attorney General was accused of "sneering" at the working-class home. When Mr Miliband heard about it, he "did not hold back in making clear how angry he was," revealed Douglas Alexander, the party's campaign chief. Ms Thornberry subsequently resigned.

The party leader stressed: "Labour's never had that view of disrespect and I'm afraid her tweet conveyed a sense of disrespect; that's not my view, that's not Labour's view, it's wrong, it never will be our view and that's why it was right she resigned."