Britain's prime minister warned Sunday that countries outside the eurozone risked being frozen out amid efforts for a pooled response to the crisis crippling the 17-nation single currency bloc.

"What you've got happening in Europe at the moment is eurozone countries coming together recognising that they've got to do more things together and frankly it's in Britain's interest that they do sort out the problems they've got," said David Cameron after a crunch EU summit.

"But there is a danger ... that as this eurozone coming together happens, there is a risk that those countries outside the euro ... might see the eurozone members starting to take decisions that affect the single market."

He stressed that he had pushed for safeguards to be included in the final statement to prevent this happening as diplomats said a row over the text had delayed the end of the meeting.

The final statement insists on "a level playing field among all member states including those not participating in the euro."

Any further coordination within the eurozone must take place in "full respect of the integrity of the European Union as a whole and its operation at 27," the statement adds.

Asked if he found it frustrating to watch decisions being taken in the eurozone without being in the room, Cameron said: "Well, no, I don't find it frustrating because I'm not in the euro and I don't want Britain to join the euro."

He stressed that Britain was a "constructive" member of the European Union and added it was in London's interest that the eurozone overcame its debt crisis, which he termed "crippling."

"In order to get a British recovery, we need to get a eurozone recovery too," said Cameron.

However, he also said that London would use any changes to the treaty to strengthen eurozone coordination as an opportunity to "repatriate powers back from the EU" to Britain.

"The key thing is this: if there is a treaty change proposal that comes forward, that gives Britain as a non euro country the opportunity to say 'well, in response to this treaty change, what's in the British national interest?'"

Britain and Denmark are the only EU countries that officially have an opt-out from joining the single currency but nations such as Sweden also show no sign of wanting to swap their national money for the crisis-hit euro.

"Right now in Sweden, the support for the Swedish currency has probably never been so high as it is now," said Swedish Prime Minister Fredrik Reinfeldt.

"The Swedish people in a referendum in 2003 said no, and we have said we would respect that until we see a clear switch in the opinion," added Reinfeldt.

Cameron is also facing pressure to hold a referendum on Britain's membership of the European Union on the eve of a non-binding but politically significant parliamentary vote on the issue.

Britain's hardline eurosceptic party on Sunday upped the ante by offering a tactical election ploy ahead of the vote in the House of Commons.

Arch-eurosceptic rivals the UK Independence Party (UKIP) said they could step aside for candidates from Cameron's Conservative party in a future election if they vote on Monday to hold the referendum.

But Cameron retorted: "I don't think this is the last time to legislate for an in-out referendum. I think this is the right time to sort out Europe's problems, sort out the eurozone problems, defend your national interest."