The U.K. is running out of bargaining chips in its "weak and pathetic" negotiations with the European Union over its terms of membership, the leader of the euroskeptic UK Independence Party, Nigel Farage, told CNBC.
Prime Minister David Cameron is holding talks to keep Britain in the European Union, with the bloc's 28 leaders suggesting there are only a few obstacles left to a new membership deal.
But Farage, who wants a political exit from Europe, says the deal being sought, which includes an "emergency brake" on benefits for migrants working and living in the U.K., is not worth seeking.
"If he (Cameron) succeeds in an emergency brake and if he succeeds in getting the migrant benefit deal he might save £50 million ($71 million). Goodness me we pay that every day to be a member of the European Union," he said.
Cameron, struggling to sell a deal to an increasingly sceptical British public and many in his own Conservative Party, has spent weeks touring European capitals to secure a deal, hold a referendum and put to rest the divisions over Europe that have dogged his party for years.
The stakes are high. A vote to leave would not only transform Britain's future role in world trade and affairs but would also shake the EU, which has struggled to maintain unity over migration and financial crises, by ripping away its second-largest economy and one of its two main military powers.
The British public is split over whether to remain in the European Union, but with opinion polls showing the 'out' campaign gaining ground, Cameron wants to hold the referendum as soon as possible..
EU officials have said there are still worries about whether some of Britain's demands will set a precedent, leading other countries to demand changes to their membership agreements.
Among the details, there will be debate over the wording of the safeguards for London's financial sector, on any commitment to future amendments of the bloc's founding treaties and on how long Britain can apply a measure to curb welfare payments for low-paid EU workers.
Farage, a campaigner for a "Brexit", said Cameron is failing to properly address the migrant issue.
"This is political. That's why we have open borders and that's the one thing the British people want addressed. He's not doing it and I would say this is a Prime Minister in some real trouble", he said.
With a prospect of late-night talks on Thursday, summit chairman Donald Tusk has scheduled what aides call an "English breakfast" on Friday in hope of a final compromise.
"The negotiations are very advanced and we must make use of the momentum," he said in an invitation letter to EU leaders.
"There will not be a better time for a compromise."
Asked if he was confident of a deal, a British government official said the prime minister thought that "we are in a good place".
The battle lines of the upcoming referendum are seen as based on the outcome of this negotiation.
London mayor Boris Johnson, seen as hugely influential in the campaign, has so far refused to commit to a position.
Mr Farage says it's time for Johnson to stand up and oppose his leader.
"This renegotiation looks so weak, so pathetic that it's virtually unsaleable.
"If Boris wants to be Prime Minister at some point in the future he has to take the opposing position to David Cameron."
Reuters contributed to this article.