UK Chancellor George Osborne will tell the European Union that Britain is likely to exit the bloc unless it overhauls its structure and the power it has over its members.
According to a number of media reports, citing officials familiar with his speech, Osborne will tell a conference that the EU has to stop resisting change and make a number of reforms, otherwise it is likely that Britain's electorate will vote to exit the 28 nation bloc.
"Our determination is clear: to deliver the reform and then let the people decide," Osborne will say.
"It is the status quo which condemns the people of Europe to an ongoing economic crisis and continuing decline. And so there is a simple choice for Europe: reform or decline."
He will add that if his and Prime Minister David Cameron's ruling Conservative party is re-elected in 2015, they will keep their promise to renegotiate the UK's EU ties before offering Britons an in/out membership referendum.
According to a number of recent polls, a slim majority said it would vote to leave the EU if it was given the chance.
While the ruling coalition party in Britain supports the country staying in the EU, it is yet to reveal what type of reforms it suggests.
Meanwhile, both pro and anti-EU groups agree that any referendum would be close.
The official, cited by a number of media outlets, said "the Chancellor will warn that the EU reform and renegotiation is necessary both for Britain's continuing membership and to avoid ongoing economic crisis and decline."
The government said a request, by 100 out of Cameron's 303 Conservative MPs, was "unrealistic" after the group wrote to him at the weekend saying they wanted the chamber to have the ability to block new EU legislation and to repeal existing measures which threatened "national interests".
"We knew there was a competitiveness problem in Europe before the crisis," Osborne will say in his speech.
"But the crisis has dramatically accelerated the shifts in the tectonic economic plates that see power moving eastwards and southwards on our planet.
"As Angela Merkel has pointed out, Europe accounts for just over 7% of the world's population, 25% of its economy, and 50% of global social welfare spending. We can't go on like this."