Britain torpedoed Belgian Prime Minister Guy Verhofstadt's bid for the European Commission presidency on Wednesday, plunging the search for a new head of the EU executive into disarray on the eve of a crucial summit.
Heavyweights France and Germany publicly back the Flemish Liberal, a keen supporter of European integration, but several states, notably those who supported the US-led war in Iraq, oppose him.
"The UK does not support Mr Verhofstadt for the presidency of the Commission," a senior British official told reporters.
He declined to give grounds other than to say "for the very obvious reason that we don't think he's the right person to be the next head of the Commission".
Although Britain has no formal veto, the move effectively kills Verhofstadt's prospects of succeeding Italy's Romano Prodi in November, diplomats said.
It also indirectly increased pressure on Luxembourg Prime Minister Jean-Claude Juncker to enter the race by highlighting the deadlock among EU leaders ahead of a two-day summit that is also due to approve a first constitution for the enlarged bloc.