Nigel Farage has demanded that the referendum on UK membership of the European Union (EU) be brought forward to July 2015 as the price for propping up a minority Tory government.
In the event of a hung parliament in next year's general election, Ukip MPs would support the Conservatives in key bills and confidence votes in exchange for the in/out referendum being held in July, two years ahead of the 2017 referendum promised by the Tories should they win.
Ukip is currently polling strongly, after its first MP, Douglas Carswell, a Tory defector, was elected to parliament last week.
A Mail on Sunday poll puts Ukip on a record 25% of the vote, and the party expects to claim between 6 and 25 seats in the general election, giving the anti-EU party the balance of power in the event of a hung parliament.
Farage said that Ukip would not enter into coalition with the Tories though.
"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," said Farage.
"I'm not prepared to wait for three years. I want to have a referendum on this great question next year, and if Ukip can maintain its momentum and get enough seats in Westminster, we might be able to achieve that.
"Some time in July next year strikes me as a very good time to do this," he told the BBC.
Prime minister David Cameron will attempt the revise the terms of Britain's membership of the EU before a referendum is held, and experts believe that Farage stands a better chance of securing an 'out' vote if that process does not take place.