Theresa May is meeting the front-runner to be the next French president for talks at 10 Downing Street.
The meeting, on Tuesday afternoon, comes as Emmanuel Macron visits London to rally support among ex-pats in the city, whose 300,000-400,000 French residents effectively make it France's sixth-largest centre of population.
French citizens overseas are entitled to vote in this spring's election to find a replacement for Francois Hollande at the Elysee Palace.
Downing Street said the Number 10 meeting had been requested by Mr Macron, who was expected to discuss "a broad range" of issues with the Prime Minister.
A former socialist, who last year established the En Marche movement to fight the presidential election, Mr Macron has come from behind to lead the polls for final victory in the two-round contest, which takes place in April and May.
A Downing Street spokesman said no other candidates had yet requested a meeting with Mrs May, but added there was a long-standing Government policy not to engage with the National Front party, whose leader Marine Le Pen is widely expected to reach the second-round run-off with Mr Macron.
Former PM Tony Blair met the centre-right's Nicolas Sarkozy at Number 10 when he was running for president in 2007, said the spokesman.
Mr Macron was later due to address 3,000 French voters in Westminster's Central Hall.
As he arrived at Number 10, Mr Macron said he wanted to discuss "the relationship between France and the UK, Brexit and some very important bilateral issues" with Mrs May.