Russia cultivated Donald Trump for years before the 2016 election and holds compromising material on the President-elect, according to a series of explosive but unconfirmed memos made public today.

The memos, produced by a British intelligence operative, contain extensive details of efforts by Russia's intelligence community, directed by Russian President Vladimir Putin, to sway the outcome of the US election.

A source told the operative that Mr Trump's "unorthodox behaviour in Russia over the years had provided the authorities there with enough embarrassing material on the [then] Republican presidential candidate to be able to blackmail him if they so wished."

The British memos, which had circulated through US political circles since before the election, contained details about extensive contact between Mr Trump and Russia in the lead-up to the campaign.