The FBI's controversial decision to re-examine Hillary Clinton's emails enabled Donald Trump to win the election, his former campaign manager has claimed.

Corey Lewandowski, who is expected to be offered a key position in the Trump administration, described the move as "amazing" and said it gave the Republican candidate the "spring in his step" he needed to win the race.

The FBI had come under intense criticism for its decision to resurrect the investigation in the eleventh hour, as Democrats said it breached impartiality rules and tipped the odds in Mr Trump's favour.

"With eleven days to go, something amazing happened," Mr Lewandowski said in a speech at the Oxford Union debating society on Wednesday evening.