The King will host EU chief Ursula von der Leyen at Windsor Castle despite warnings that the meeting will drag the monarchy into the political announcement of a new Brexit deal.

Charles and the European Commission president will sit down for tea late on Monday after she is expected to sign off on a Northern Ireland Protocol agreement with Rishi Sunak.

There were fears the King, who as head of state must remain politically neutral, might be drawn into the process of the UK and EU agreeing the new deal or be seen as tacitly endorsing it.

Buckingham Palace said Charles was acting on “the Government’s advice” and that their discussions would feature a “range of topics”.

Downing Street said it was “fundamentally” a decision for Buckingham Palace.

Baroness Arlene Foster, the former DUP leader and first minister of Northern Ireland, said: “I cannot quite believe that No 10 would ask HM the King to become involved in the finalising of a deal as controversial as this one. It’s crass and will go down very badly in NI.

“We must remember this is not the King’s decision but the Government who it appears are tone deaf.”

Conservatives were among those voicing their criticism of the meeting before it was even confirmed, following suggestions the deal would be called the “Windsor Agreement”.

Leading Tory Brexiteer Jacob Rees-Mogg said it would be a mistake for Ms von der Leyen to meet the King during her visit to the UK.

The former Cabinet minister told GB News: “I think the sovereign should only be involved when things have been completed and accepted.

“The King gives assent to acts of Parliament when Parliament has agreed, he doesn’t express his view on acts of Parliament when they are going through the process.

“I think the same applies – that His Majesty should not be involved until there is full support for this agreement.”

Sammy Wilson, the chief whip of the Democratic Unionist Party (DUP), which the Prime Minister wants to secure the support of, said the expected meeting risked “dragging the King into a hugely controversial political issue”.

Downing Street has defended the decision to advise the King to meet Ms von der Leyen, saying Mr Sunak “fundamentally” believes the final decision was for the King.

“He firmly believes it’s for the King to make those decisions,” the Prime Minister’s official spokesman said.

He compared the von der Leyen meeting to Charles talking to Poland’s Andrzej Duda or Ukraine’s president, Volodymyr Zelensky.

“It’s not uncommon for his majesty to accept invitations to meet certain leaders, he has met President Duda and President Zelensky recently. He is meeting with the president of the EU today,” the spokesman said.

Asked why the final protocol talks were taking place in Windsor, he said: “There are a number of occasions when these sorts of talks have been held in significant locations, this is no different.”

Topics up for discussion between Charles and the EU chief include climate change and the Russian invasion of Ukraine, though it was unknown if they will discuss Northern Ireland.

A Buckingham Palace spokesman said: “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.”

Charles and Ms von der Leyen will meet at Windsor Castle once her commitments elsewhere have been fulfilled.