Britain is on course for a showdown with the United Nations over the choice of the next Secretary-General, after sources in Washington indicated that the US was preparing to throw its weight behind the candidate from Argentina.

Susana Malcorra, currently serving as Argentina’s foreign minister, is understood to have received top-level backing from both the White House and Susan Rice, national security adviser to Barack Obama.

The prospect of an Argentine leading the UN presents Britain with a diplomatic dilemma given the long-running dispute over the Falklands which both Argentina and the UN say must be “decolonised” and returned to Argentina.

President Barack Obama is said to have been won over by arguments in Ms Malcorra’s favour from his Argentine counterpart Mauricio Macri on a visit to Buenos Aires in March that was widely seen as an attempt to re-set US-Argentinian relations.