The president of Singapore, Tony Tan Keng Yam, rides in a carriage with Britain’s Queen Elizabeth II during a state visit in October 2014. (Toby Melville/Reuters)

British lawmakers on Monday will debate whether to withdraw an invitation to President Trump for a state visit — ­an offer extended with un­precedented speed.

The debate, to be held in Parliament’s Westminster Hall, was triggered after a petition calling on the British government to cancel the state visit amassed more than 1.8 million signatures. A counter-petition urging the government to support the visit, signed by 300,000, will also be debated.

Although many of Europe’s leaders were unenthusiastic about Trump’s election victory, British Prime Minister Theresa May has sought to curry favor with the new U.S. president. May was the first foreign leader to meet with Trump at the White House, and she wasted little time in offering him the royal treatment in the form of a full state visit, at a date to be determined.

That decision has proved polarizing. After Trump’s executive order temporarily banning U.S. entry to citizens from seven Muslim-majority nations, the signature count on the petitions grew rapidly. The ban has since been suspended by U.S. courts.

Although the travel ban was widely condemned in Britain, a recent poll found that more people were in favor of Britain rolling out the red carpet for Trump than were against it. ­According to the Ipsos ­MORI-Evening Standard survey, 53 percent of Britons support the visit and 42 percent oppose it.

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“Opinion in Britain is very divided,” said Tim Bale, a politics expert at London’s Queen Mary University. “People look at Trump with fascination. For some, it’s horrified fascination. Others admire him as a ballsy, . . . can-do guy who says a lot of things that many people think.”

Bale said that May’s courting of Trump was probably driven by the Brexit vote and by Britain’s need to cement alliances with new ­trading partners after it leaves the European Union. Offering the state visit so soon, Bale said, “probably had to do with an assessment of Trump’s character that this is someone who is susceptible to flattery.”

Trump has spoken warmly about Britain, where he owns two golf resorts, and reportedly told May shortly after he won the ­election that his Scottish-born mother was a “big fan” of Queen Elizabeth II.

He is not the first U.S. president to be accorded a full state visit to Britain, traditionally including a horse-drawn-carriage ride with the queen and a formal banquet at Buckingham Palace. But he is the first to be invited within a week of his inauguration.

President George W. Bush waited 978 days after taking office for his invitation, and President Barack Obama waited 758 days.

Asked about the timing, a Downing Street spokeswoman said: “There isn’t a set process. There isn’t a criteria set down that says X leader from X country needs to serve X days in office beforehand.”

But for some, May acted too hastily.

“It is a uniquely maladroit invitation because of its timing — there is no precedence,” said Paul Flynn, a lawmaker for the opposition Labour Party and member of the Petitions Committee.

Flynn, who will lead off the debate Monday, said in an ­interview that if Trump “had been president for four or five years, and generally there was this idea that we could rub along with you, then that’s one thing. But there is no precedent for inviting ­someone seven days after the inauguration.”

The petition calling for the state visit to be canceled — the second-biggest petition ever on Parliament’s website — does not seek to ban Trump from traveling to Britain. (A petition seeking that was debated by lawmakers last year.) But it does say that he should not be offered a full state visit over concerns that it could prove embarrassing for the queen.

The British royal family has long been viewed as an asset by British prime ministers, who are prepared to call on the royals to help bolster diplomatic and ­economic relations. The queen acts as host during a state visit, but the invitation itself is made on the recommendation of the government.

The queen’s state carriage has ferried a number of controversial world leaders over the years, including the Romanian dictator Nicolae Ceausescu and Zimbabwe’s Robert Mugabe. When Bush came in 2003, thousands took to the streets to protest the Iraq War.

“A Queen who has been asked over the decades to host tyrants such as Presidents Mobutu of Zaire and Ceausescu of Romania is going to take a brash billionaire from New York effortlessly in her stride,” William Hague, a former foreign secretary, wrote in the Daily Telegraph.

The date and details of Trump’s state visit have yet to be announced, but according to the ­Ipsos MORI-Evening Standard poll, a slim majority of Britons don’t think Trump should be allowed to address lawmakers in Parliament, as Obama did during his state visit in 2011.

There has been no indication that this is something Trump wants to do, and it may not be an option anyway.

In a surprise intervention, John Bercow, the speaker of the House of Commons, recently cited Trump’s “racism and sexism” as reasons he would try to prevent such an address.

Still, the government has been clear that the visit will proceed.

“Of course we recognize there are differing views around it, and people have a right to peacefully protest and express those views,” the prime minister’s spokes­woman said recently. “But the state visit stands.”