Labour and the Conservatives will seek to recapture the political agenda today as Tory defector Douglas Carswell returns to Parliament as Ukip's first directly-elected MP.
Both parties are attempting to halt the Ukip juggernaut after being left bruised at the hands of the Eurosceptics in last week's by-elections.
Boris Johnson has underlined his calls for Britain to be ready to quit the European Union and demanded curbs on freedom of movement as he made his pitch to win back disaffected voters.
In his regular column for the Daily Telegragh, the Mayor of London wr ote: "It is only reasonable for us to have some kind of further protections - involving points or even quotas, agreed with business - so that we can manage this pressure. It would be madness to close our borders to talent; but it is also madness to continue with a system that means we have no idea how many are coming or what burdens they may place on the state.
"Only David Cameron can conceivably deliver those changes, since he is the only leader who can lead reform of the EU. That is the point I hope the kippers (Ukip) will recognise in May next year. And the rest of us should recognise, in turn, that the kippers aren't wicked. They don't hate immigrants; they just hate the lack of control of immigration."
Ed Miliband will face restive backbenchers at a meeting of the Parliamentary Labour Party tonight after his party came within a whisker of losing the Heywood and Middleton by-election.
Deputy leader Harriet Harman insisted there was no "wobble" in the Labour ranks and denied a leadership change would be required despite concerns about how voters view the party.
Meanwhile, Nigel Farage has said Ukip would prop up a minority Conservative government if the Tories agreed to a swift and fair referendum on Britain's membership of the European Union. The Ukip leader accused David Cameron of trying to kick the national vote, planned for 2017 if the Tories win outright next May, "into the long grass".
But the anti-Brussels party would agree to a confidence and supply arrangement - where it backs or abstains on budget and legislative programme votes - with a minority Conservative government in return for a full referendum in July next year.
Mr Farage told BBC1's Sunday Politics: "The price would be a full, free and fair referendum on our continued membership of the European Union, the opportunity to get our country back, and for that to happen quickly."
The next by-election battle, which will be fought in Rochester and Strood, could lead to either Mr Cameron and Mr Miliband being ousted if their parties are given a further drubbing, he claimed.
Pressed on who he would prefer to be prime minister after the general election, Mr Farage told the programme: "Ask me that after the Rochester by-election because I think there is a possibility that one or both of those leaders may not be leading their parties in to the next general election."
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