TONY Blair emerged from a gruelling round of negotiations in Luxembourg last night claiming a victory in his fight to win Britain a seat on a powerful new single currency committee, writes Benedict Brogan, Political Editor.

However the French and Dutch governments immediately cast doubts on the Prime Minister's optimistic interpretation of events and warned the UK would remain firmly on the periphery of Europe as long as it stays out of monetary union. With the initiative swinging to and fro throughout the talks, Mr Blair at times appeared close to the isolation more typical of the Tories in Europe.

A compromise deal brokered during the first day of the EU summit confirmed that all 15 member states would be allowed a voice on the Euro-X committee which will play a key role in setting policy on monetary union.

Britain feared the committee could emerge as a rival decision-making body to Ecofin, the monthly meeting of all 15 European finance Ministers which sets policy.

A deal was sealed after Germany urged a compromise should be reached last night. As a result decisions on the details have effectively been deferred.

The summit accord states that: ''Whenever issues of common interest are discussed the Ministers of all 15 member states will participate.''

Although the UK failed to stop the new ''club'' being created, British officials claimed the deal amounted to a concession by the French, who had opposed allowing Britain a seat on the committee because it had no plans to join the single currency.

They said ''common interest'' would be strictly defined to limit the number of times the Euro-X committee would meet, ensuring the regular meetings of Ecofin would remain the decision-making body for policy on Economic and Monetary Union (Emu).

But it emerged last night that the accord remained open to wide interpretation as diplomats struggled to come up with a definition of ''common interest''. Government sources conceded the definition of ''common interests'' was not narrow.

Last night Mr Blair said: ''I am absolutely delighted this has been resolved. This is a perfectly sensible agreement. Ecofin is the only decision-making body. That is something we have consistently been insisting upon and, in all matters of common interest, all 15 have the right to participate whether in Ecofin or Euro X.''

The row, which threatens to spill over into the six-month presidency of the EU, which begins on January 1, centres on French-led plans to set up a separate ''club'' to manage the single currency.

France, backed by Germany and other countries committed to joining the single currency, wants Euro-X to be made up solely of ''ins'' - countries in EMU.

Mr Blair argues the decisions about the single currency could have substantial effects on the economies of the four countries which have so far refused to join: the UK, Sweden, Denmark and Greece.

By lunchtime yesterday Mr Blair had dug in his heels and was refusing to compromise on his insistence that Britain could not be excluded from Euro-X meetings.