It was a chance romantic encounter by George Papadopoulos that set in train the events that led to the Australian government tipping off Washington about what it knew of Russian hacking efforts to swing the US presidential election.

Fairfax Media can reveal a woman in London with whom Papadopoulos became involved happened to know Alexander Downer and told the Australian High Commissioner about Papadopoulos, a newly signed staffer for Donald Trump. Downer, being a canny diplomat, followed it up and arranged a meeting with the young American, who was mostly living in London at the time.

What followed was the now infamous May 2016 conversation over many glasses of wine at the swanky Kensington Wine Rooms, during which the 28-year-old Papadopoulos spilled to Downer that he knew of a Russian dirt file on the rival Clinton campaign consisting of thousands of hacked emails.

That night was a key moment that helped spark the FBI probe - since taken over by respected former FBI director Robert Mueller as a special counsel - into possible Trump campaign collusion with the Kremlin, including its hacking of the Democratic National Committee.