The US embassy in London is to relocate from the glamorous environs of Mayfair to the more gritty “Nine Elms” quarter in Vauxhall, south of the river Thames.

Robert Tuttle, the US ambassador to the UK, said on Thursday afternoon that he had signed a conditional agreement with Ballymore, an Irish property developer, to acquire the new site. Nine Elms is not far from the headquarters of MI6, the secret intelligence service.