Nick Clegg will veto any proposals by the Conservatives to repatriate powers from Europe if treaty renegotiations are needed to save the eurozone.
Party officials said Mr Clegg had made it clear to David Cameron that any attempt to translate euro-sceptic Tory rhetoric into policy would be opposed by the Liberal Democrats. Mr Clegg is expected to address the question of Europe in his speech on Wednesday and will stress the need to help eurozone countries rather than use the crisis to leverage powers from Brussels.
The Lib Dem leadership expects the issue of Europe to dominate the Conservative conference in Manchester the week after next, and are expecting tough words from the leadership to appease the party faithful.
But they are insistent that this should not be fed through into policymaking or the position of the Government in dealing with the European financial crisis, which is likely to dominate autumn's political agenda.
"It's natural in the conference season for parties to appeal to their base," said a Liberal Democrat source. "And there is no doubt that Europe is one area where we disagree fundamentally. So far that has not mattered too much, but we are clear that if it comes to it we will fight any attempt to move away from our current commitment to the EU."
In a sign of Lib Dem ministers' determination not to cede ground on the European issue, Danny Alexander, Chief Secretary to the Treasury, used his speech to pledge that he would never let "anti-European isolationists frustrate our national interest".
"As the eurozone seeks to deepen its integration they will need our support and they will get it," he said. "Sadly, euro-sceptics still fail to understand that sharing sovereignty strengthens our influence and isolation weakens us."
Mr Alexander praised the "practical, pragmatic engagement" of Mr Cameron and Mr Osborne in dealing with Brussels.
But, in an interview on the BBC's Andrew Marr Show, Mr Clegg said that the "greatest achievement" in European integration was the creation of the single European market and nothing should be done to jeopardise it.
They are the loyal supporters who, a year ago, were still riding high from their party's unlikely journey into government. But a year on, how do Lib Dem voters feel now the conference season has arrived?
Margie Arts, 69, retired lollypop lady, Cumbria
The Lib Dems do not have the numbers in Parliament to be able to make changes. We have seen it with the NHS. Nick Clegg attempts to say he opposes the Conservative changes but he has done little to stop them. I voted Lib Dem in the last election because my local candidate Barry Rabone was a good honest man. The crackdown on the 50p tax is a good start, but it will need more on a national level if Nick Clegg is to keep my vote.
Sam Raper, 45, school bursar, Manchester
Nick Clegg is too contradictory. One minute he says he won't go in with the euro. Then he says he's not opposed to it in principle. I was expecting big things from the first day of the conference, but the tax crackdown on the rich is not clear. And meeting with Hugh Grant is just ridiculous. I want to see some bolder ideas like cutting university fees in half or a clear plan for the next few years that shows the party is listening. It's a coalition, but both parties feel like they're too far apart.
Malcolm Kirby, 70, retired company director, Norfolk
The Lib Dems have had a difficult year but things would have been a lot worse had they not been in power. Had the Tories been solely in charge, the cuts would have been deeper and faster. Despite a tough year, the party has plenty of local support and it is up to the higher tiers to mirror that. The country is better off with another party to hold the Conservatives to account.
Gez Smith, 32, e-participation consultant, Bristol
In the last six months I feel a lot happier with the party's performance. The party showed huge political naivety over tuition fees. Instead of voting against it, they could have abstained altogether. During this conference I want to see distinctive policy announcements that show they are able to stand up to the Tories and that lessons have been learned.
Ashley Evans, 26, Solihull
I am not impressed. The party has gone back on pledges like tuition fees, and lost trust as a result. Nick Clegg seems to be Cameron's 'yes' man – a far cry from the TV debates which painted him as a dynamic leader. I think the coalition has sounded the death knell for the Lib Dems. It could be 10 years until they are ever in contention for power again.Reuse content