Sir Nigel Sheinwald, Tony Blair’s Downing Street foreign policy adviser, is set to take over as Britain’s ambassador to the US next year.

Sir David Manning, the current ambassador, who was also the prime minister’s foreign policy adviser, intends to step down next spring and does not wish to continue after Blair’s departure. Reports suggest that Sir Nigel’s appointment, which the prime minister hopes to confirm before he leaves office, would reassure the Bush administration of continuity of relations with Britain under a Gordon Brown premiership.

Under the FCO’s procedures, top posts are filled after a shortlist of candidates is considered by an appointments board, which includes the foreign secretary. Sir Nigel, 53, has previously servced as Britain’s envoy to the EU and as a Foreign Office spokesman.