David Cameron refuses more euro bail-outs
The UK supports a strong eurozone but will "not be drawn into" funding agreements to bail out any more failing economies, David Cameron has said.
The prime minister, after talks with French counterpart Francois Fillon, added that the UK would never join the euro under his leadership.
But he said relations with France were currently "very, very strong".
Mr Fillon said eurozone "harmonisation" would increase but he understood the "British want to remain British".
The single currency has come under strain after the European Union bailed out debt-plagued Greece and Ireland, and with fears over the future of other economies, including those of Portugal and Spain.
The Downing Street press conference came after talks between Mr Cameron and Mr Fillon about financial reform and the state of the 17-member eurozone.
It also followed the publication of a Times interview in which Mr Fillon called for the UK to play a more "proactive" role in Europe and to accept that there would be greater economic integration of nations already in the single currency.
Mr Cameron said: "Let me be absolutely clear: Britain is not a member of the eurozone and we're not going to join the eurozone as long as I'm prime minister. That's not going to happen."
He added: "A strong and safe harmonisation is in the eurozone's interest. We want the countries of the eurozone to sort out the problems they have. We won't stand in the way and will be a helpful partner...
"We want a strong eurozone and want it to sort out its problems, but we are not joining the eurozone and won't be drawn into fresh and new mechanisms for [bailing out the] eurozone."
Mr Fillon, who has been French Prime Minister since 2007, said: "I've asked the UK to look at the arguments for harmonisation in a favourable light."
He added: "We mustn't exaggerate the differences between our two countries."
He also said: "I'm not asking the UK to join the eurozone."
In his Times interview, Mr Fillon said it would be a "catastrophe and a disaster" for the UK if the single currency failed.
He said: "The question is: is the UK ready to accept or encourage greater integration of the eurozone or is the UK distrustful of that and will it make it more difficult to happen."
Mr Cameron pledged to keep the UK out of the euro at the last general election.
The subsequent coalition agreement with the Lib Dems promises the government will be a "positive participant in the European Union, playing a strong and positive role with our partners".
But it rules out joining the euro during this parliament and pledges to "ensure that there is no further transfer of sovereignty or powers" during the same period.
The European Union Bill, backed by the House of Commons earlier this week, says a referendum will be required in future whenever "significant" powers are passed to Brussels in future.
Ministers say the plan for a "referendum lock" will help preserve national sovereignty.
However, some Conservative MPs argue that the wording of the legislation means the government will get the ultimate say on which issues go to a public vote, making it less democratic.
Mr Cameron will be holding talks later with European Council President Herman Van Rompuy about the future of the euro.