British Prime Minister David Cameron is "sleepwalking" toward an exit from the EU by pushing his plans to repatriate powers from the bloc, opposition leader Ed Miliband said Sunday.
The Labour leader's comments added to the pressure on Conservative Cameron as he prepares to make a speech this month in which he is expected to propose a referendum after 2015 on the conditions of Britain's EU membership.
"I think it's incredibly dangerous what David Cameron's doing. I think he is essentially sleepwalking us towards the exit door from the European Union," Miliband told the BBC.
"It's the wrong thing to do, it's not in the national interest."
Cameron's plan "means that you are having a referendum on a negotiation that has not yet begun, with a timescale that is uncertain and an outcome that is unknown and that is an incredible gamble," Miliband added.
The prime minister's long-awaited speech -- reportedly due to take place on January 22 in an unspecified European city -- has raised fears at home and abroad of a so-called "Brexit" from the group.
Ireland's deputy prime minister Eamon Gilmore on Sunday joined a growing chorus in the 27-member bloc saying that Britain could not pick and choose the terms of its EU membership.
"Where there cannot be flexibility is on the core conditions of membership. You cannot have a European Union if you end up with 27 different forms of membership," Gilmore told Sky News.
Austrian Chancellor Werner Faymann accused Cameron on Friday of sending mixed messages on the EU and a senior German lawmaker warned him against "blackmailing" the bloc.
The United States, Britain's closest ally, also unexpectedly joined the fray, with a US official earlier this week expressing concern about Cameron's plans.
At home, Cameron is under pressure from the increasingly eurosceptic right wing of his Conservative party, and from opinion polls suggesting growing hostility to the EU in Britain.
But there have also been signs of a pro-EU camp starting to get organised.
Heavyweight British political rivals Kenneth Clarke, a Conservative, and Peter Mandelson, from Labour, are to join forces to lobby for Britain to stay within the EU, the Observer newspaper reported Sunday.
Chris Rennard, a peer with the Liberal Democrat party that is in coalition with the Conservatives, will join Clarke and Labour grandee Mandelson in fronting the Centre for British Influence through Europe (CBIE).
The organisation will be launched at the end of the month, according to the report.
CBIE director Peter Wilding said he hoped for a mature debate on the bloc's future.
"Both Mandelson and Rennard are closely involved in our policy and campaign strategy," he told the Observer.
British business leaders wrote an open letter to Cameron this week warning that a renegotiation of membership risked an exit from Europe, with "damaging" consequences for the economy.
Conservative veteran and former minister Michael Heseltine -- who helped topple former premier Margaret Thatcher over the issue of Europe -- on Saturday described Downing Street's position as "ill-advised".