Washington is due to nominate the head of finance of Barack Obama's re-election campaign, Matthew Barzun, as the new US ambassador to London, according to diplomatic sources.

Barzun's nomination has been delayed by the general backlog of personnel appointments at the state department as it looks around for new faces to fill critical roles in Obama's second administration, but it is said now to be imminent.

Barzun, 42, is a Kentucky-based businessman who was made ambassador to Sweden in 2009 in recognition of his work on the 2008 Obama campaign, where he won praise for amassing large numbers of small scale contributors. But he was called back to the US two years later to lead the fundraising drive for the 2012 campaign, the most expensive in US history. The campaign Barzun ran raised $730m (£470m)....