Germany and France have united against Britain's attempts to gain more concessions on the EU constitution.

During a meeting of EU foreign ministers in Brussels, Jack Straw, the foreign secretary, demanded extra assurances that the Charter of Fundamental Rights would not become a legally enforceable part of the constitution.

Joschka Fischer and Michel Barnier, Straw's German and French counterparts, said that Britain had already won major concessions last year and could not now come back for more.

"It was... a marker of Franco-German exasperation at Britain's decision to call a referendum," one diplomat said.

"It was a way of telling the British that just because you are having a referendum does not mean that you can open some new credit line on which you can draw more concessions."