LONDON—The British government’s decision to invite U.S. President Donald Trump for a state visit, one of the highest honours it can bestow on a visiting statesman, has involved Queen Elizabeth II in the passionate debate over Trump’s travel ban.

Trump’s provocative decision to deny refugees access to the United States and to make it more difficult for people from seven Muslim-majority countries to visit has been widely denounced by opposition leaders and sparked protests in British cities and campuses, leading some to question the wisdom of the government’s decision. Some 1.6 million people in the U.K. have also signed a parliamentary petition calling for the invitation extended by Prime Minister Theresa May to be withdrawn.

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Prince Charles even weighed in on the controversy, saying he fears the lessons of Second World War have been forgotten.

“The work of World Jewish Relief enables us to rally together, to do what we can to support people practically, emotionally and spiritually,” the prince said in speech at a Jewish charity’s dinner on Monday night. “Particularly at a time when the horrific lessons of the last war seem to be in increasing danger of being forgotten.”

While the queen has steered clear of any political commentary, her son, on the other hand, does speak out on issues he feels passionately about, such as climate change and religious persecution. The Sunday Times reported that if the visit went ahead, Charles planned to confront Trump over global warming.

It is the British government that invites heads of state on the queen’s behalf, but it is the queen who acts as personal hostess. In most cases, that involves lavish pomp and ceremony and a stay of several days at the queen’s official residence, Buckingham Palace.

The prospect of protests outside the palace when Trump comes calling has put the queen in a “very difficult position,” said Peter Ricketts, formerly a top official in the Foreign Office.

In a letter to The Times Tuesday, Ricketts said the “state visit” should be downgraded to a lower level “official visit” to spare the monarch any embarrassment. He said the offer should not have been made in the first days of Trump’s administration.

“It would have been far wiser to wait and see what sort of president he would turn out to be before advising the queen to invite him,” Ricketts said.

London Mayor Sadiq Khan, the first Muslim elected to that post, has called for the invitation to be rescinded. His office said he will describe Trump's travel ban as "cruel, prejudiced and counterproductive" at a City Hall diplomatic reception Tuesday.

The online petition opposing Trump’s visit has prompted what will be a non-binding debate in Parliament set for Feb. 20.

State visits are typically offered to foreign monarchs, presidents and prime ministers in ways designed to bolster British diplomacy and economic interests.

The invitation to Trump is part of an effort to strengthen ties with the goal of reaching a beneficial trade agreement with the United States once Britain leaves the European Union.

A state visit is a carefully choreographed event and involves grand pageantry in the heart of London.

The queen and other senior royals greet visitors with a ceremonial welcome, usually on Horse Guards Parade, followed by a carriage procession to the palace. A multi-gun salute is fired from Green Park and the Tower of London, and there is traditionally a formal banquet with roughly 150 guests gathered in the palace ballroom.

The queen opens proceedings with a speech, followed by a formal toast to her guest.

Buckingham Palace officials said the queen would not comment on the state dinner plans. The government says the visit is “months away” and that a date has not been chosen.

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May said during a joint appearance with Trump Friday that he would be coming for a state visit at an unspecified date.

Hours later, Trump signed the executive order limiting travel to the United States. May has said she does not agree with the plan, but the government insists the state visit is going forward.

With files from Bloomberg

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