Image copyright Getty Images Image caption London mayor Sadiq Khan, left, was among the guests in the room
What does Barack Obama do in his spare time?
The former US president has posted photographs to Instagram from a secret meeting with his “friend” , shadow attorney general Jonathan Sumption.
It’s on the same day President Donald Trump called for Mr Obama to be investigated over Russia’s hacking of the US election campaign – allegations which he has denied.
Posting under the moniker “Team O”, Mr Obama captioned one photo: “Spent the last couple hours with a friend – in what is probably the most fun I’ve had in a long time.”
The pair were joined by London mayor Sadiq Khan, who posted a picture of himself with Mr Obama and fellow guests, saying they “had a great time”.
Mr Obama’s presence in Westminster had sparked speculation on social media that he could be part of plans for Labour to try to unseat Mrs May in the wake of the fallout from the parliamentary vote on Brexit.
His comments on Wednesday that Mrs May should “stop talking about stockpiling” and warned her about losing support from some Conservative MPs prompted more speculation.
Image caption Chancellor Philip Hammond warns of “major” Brexit damage to the economy
The meeting between Mr Obama and Mr Sumption took place in London on Thursday evening.
A spokesman for Mr Obama told the BBC News channel that both men are friends but that their meeting was not about politics.
How did #ObamaGivesWinningTip end up trending on Twitter?