Brown was one of eight socialist heads of government meeting to agree a common position on candidates for two new EU jobs ahead of a full Brussels summit, and the spokesman said the British premier realised Blair would not get the required backing during their talks.

"As it became clear that the chances for a Blair presidency were declining the prime minister made the decisive intervention in this meeting, to ensure that the high representative role is going to be a British representative," the spokesman said.

"I can not see any opposition from any other member state to her securing the post," he added.

Ashton, currently in charge of trade at the European Commission, gets Brown′s nomination ahead of his Foreign Secretary David Miliband -- originally the preferred choice for many among Brown′s socialist partners.

But with the backing of eight European governments -- and convention dictating that the centre-left grouping essentially gets to choose the job of foreign policy supremo -- Brown gets to lay claim to major influence at the heart of a new-look Brussels set-up.

"In the time she has been here (Brussels) she has created a very strong impression. She is someone who is well respected in the corridors of Brussels... She will be a big player and the United Kingdom is delighted to support her," Downing Street said.

"We feel that it is in Britain′s interests to play a major role in the new EU and don′t forget this is a very important job -- not just for its political role but also for its defence role," the spokesman added.

Nonetheless, Ashton has detractors among political rivals -- with one European diplomat, from a different end on the political spectrum, saying her nomination by London had set Europe back years on the international stage.

"The British wanted to kill the post" of high representative, said the diplomat.

"They have succeeded. This will set us back five years."

On who will now claim the top job of EU president, Downing Street said it was up to their centre-right partners to settle that decision -- putting Belgian Prime Minister Herman Van Rompuy clearly in the driving seat.

"We have to see the candidates," the spokesman underlined, "but it is now down to the EPP (the grouping of conservative-led countries) to make their decision."

However the spokesman downplayed the stature of the top job, suggesting it wasn′t substantial enough for Blair.

"The role of president is quite obviously a different role than the big president role it was originally perceived to be, so for someone like Tony Blair there′s a factor there about the kind of size and scale of the role," he asserted.

The post was created by the Lisbon Treaty, which comes into force on December 1. The ′high representative,′ as she is officially known, is meant to help give the EU a higher profile abroad and to make its foreign policy more coherent.