Prime Minister David Cameron will get a hero's welcome from his party but faces a backlash from his Liberal Democrat allies Monday when he explains a European Union veto that has cast Britain adrift from its continental partners.

Cameron's decision not to take part in an EU treaty change aimed at tightening fiscal rules for countries using the euro has isolated Britain in the 27-nation bloc and created the biggest rift in his coalition since he took power in May 2010.

Cameron's deputy Nick Clegg said Sunday he was bitterly disappointed with the outcome of the summit, which he said was bad for Britain.

Clegg leads the pro-European Liberal Democrats, the junior partners in an uneasy alliance which has vowed to rule until the next election due in 2015.

Despite his anger over Europe, Clegg said it would be an economic disaster were the coalition - which has imposed harsh spending cuts to fight a record budget deficit - to fall apart now when the economy is teetering on the edge of recession.

The Liberal Democrats have seen their poll ratings slide to little more than 10 percent since the election, down by more than a half, and Clegg knows that a snap poll would leave them facing another long spell in the political wilderness.

At the Brussels summit Friday, Britain vetoed a plan for a new EU treaty that would impose closer EU control over national government budgets to curb the bloc's debt crisis. Cameron said the proposed deal risked exposing London's powerful financial services industry to unwelcome EU regulation.

The other member states, including the 17 using the euro, now plan to adopt a separate pact without Britain, leaving the island nation alone as never before in the EU, a club it joined in 1973 but which Britons have long viewed with distrust.

Cameron will address parliament at 1530 GMT Monday afternoon to explain the outcome of the summit.

Basically he'll reiterate what he's said over the last couple of days about why he did what he did and why he thought it was the right thing to do, said a spokesman for his Downing Street office.

Britain is not a member of the euro. What they were debating about is how they are organised to make sure that the euro works, he added. In terms of other types of policy, defence, all sorts of other policy, Britain will still be very much at the centre of things.

BULLDOG SPIRIT

Conservative eurosceptics in parliament had last week sent Cameron on his way to Brussels with a plea to show some bulldog spirit by standing up for Britain.

A former public relations executive, Cameron will need all his presentational skills to get the tone right Monday.

If he comes back trying to present this as triumphalist, as some kind of victory for the 'bulldog spirit', I think that will go down badly with Lib Dems, said Liberal Democrat parliamentarian Martin Horwood.

There is a very united tone within the Lib Dems, and it is overwhelmingly one of disappointment at the outcome, he told Reuters.

The real question is why Mr Cameron emerged with no friends at all in that negotiating chamber. I would say the extreme eurosceptic antics in the run up to the summit had a lot to do with that.

Europe has long been a toxic issue for the Conservatives, having divided the centre-right party in the 1990s when it was last in power.

Eighty-one Conservative parliamentarians - more than a quarter of the total - defied Cameron in October and backed calls for a referendum on Britain's EU membership, a demand which resonates with voters at a time when the euro zone is struggling.

Cameron's critics in the opposition Labour party have accused him of caving in to domestic pressure and believe his restive right-wing will press for more concessions.

One of the difficulties for David Cameron is he hasn't sated the appetite of the eurosceptics on his back benches. He will simply have encouraged them, Douglas Alexander, Labour foreign affairs spokesman, told BBC TV.

I don't believe right now the priority for Britain, when we're struggling to see growth in an economy that's flat lining, would be to spend the next few months negotiating and discussing a referendum on the European Union, added Alexander.

(Additional reporting by Mohammed Abbas, Tim Castle and Stefano Ambrogi; Editing by Peter Graff)