The president of the European Commission will meet King Charles on Monday during a visit to Britain to discuss an overhaul of the post-Brexit trade rules for Northern Ireland.

"The president will also meet this afternoon His Majesty the King," EU spokeswoman Dana Spinant told reporters, in an update to Ursula von der Leyen's talks with British premier Rishi Sunak.

Buckingham Palace confirmed the meeting.

"The King is pleased to meet any world leader if they are visiting Britain and it is the government's advice that he should do so," a spokesman told reporters. 

"The head of state and president will sit down to tea late on Monday afternoon during their meeting where a range of topics are expected to be discussed, including climate change and the situation in Ukraine." 

Von der Leyen tweeted a picture of herself descending from a cross-Channel train in London, but made no mention of the royal leg of her trip. 

"I'm glad to be in the UK today to meet with Prime Minister Rishi Sunak," she wrote "I'm looking forward to turning a page and opening a new chapter with our partner and friend." 

The two were due to hold what they've called "final talks" before unveiling changes to post-Brexit trade rules for Northern Ireland, a breakthrough aimed at rebuilding strained relations.

But, while the reforms to the "Northern Ireland Protocol" are understood to be more or less agreed between Brussels and London, Sunak faces a battle to win approval at home.  

Politicians from Northern Ireland's pro-British unionist community and some MPs from Sunak's own Conservative Party, including former prime minister Boris Johnson, are pushing for a harder line.