[LONDON] Donald Trump promised Britain a substantial post-Brexit trade deal with the United States on Tuesday, quipping to outgoing Prime Minister Theresa May that she should stick around to clinch it though she is due to step down in two days' time.

Feted by Queen Elizabeth on the first day of his state visit to Britain, Mr Trump turned to politics on Tuesday, potentially meeting candidates vying to succeed May and a discussion about the role China's Huawei should have in building 5G networks.

Even before Air Force One landed on British soil, Mr Trump praised the main leaders of Brexit - Boris Johnson and Nigel Farage - and his advisers called on Britain's next leader to block Huawei from the next generation mobile phone technology.

"We'll have a very, very substantial trade deal, it'll be a very fair deal, and I think it's something we both want to do," Mr Trump told May at a meeting in St James's Palace, a 500-year-old official residence of the monarch.

"I don't know exactly what your timing is, but stick around. Let's do this deal," Mr Trump said. Mrs May is due to resign as Conservative Party leader on Friday, but will remain as prime minister while a contest is held to replace her.

Mrs May said Britain and the United States should work together to keep markets free, fair and open.

The state visit, promised by Mrs May back in January 2017 when she became the first foreign leader to meet him after he took office, is cast as a chance to celebrate Britain's "special relationship" with the United States, boost trade links and reaffirm security cooperation.

But the collapse of Mrs May's premiership over Brexit and Mr Trump's penchant for ignoring the conventions of modern diplomacy have made the trip one of the most unconventional state visits in recent British history.

Ahead of the visit, Mr Trump praised Mr Johnson, the former foreign secretary and leading Brexit campaigner, and advised a sharp exit from the European Union on Oct. 31 with or without a deal.

Mr Trump also called for arch-Brexiteer Farage, a scourge of Mrs May's ruling Conservative Party, to conduct talks with the EU.

Brexit is the most significant geopolitical move for the United Kingdom since World War Two and if it happens, London will be more reliant on the United States as ties loosen with the other 27 members of the EU.

Huawei will top talks in London after the British government appeared to defy Trump administration demands and allow the Chinese company a limited role in building 5G networks.

"We've been clear: Our ask is that our allies and our partners and our friends don't do anything that would endanger our shared security interests or restrict our ability to share sensitive information," US Secretary of State Mike Pompeo said.

The Trump administration has told allies not to use Huawei's 5G technology and equipment because it fears that would allow China to spy on sensitive communications and data. Huawei denies it is, or could be, a vehicle for Chinese intelligence.

Notwithstanding Britain's enduring alliance with the United States, some British voters see Mr Trump as crude, volatile and opposed to their values on issues ranging from global warming to his treatment of women.

Thousands of people protested in central London on Tuesday against Mr Trump's pomp-laden state visit to Britain, but numbers were far down from the tens of thousands who gathered to oppose his visit last year.

Protesters waved witty and sometimes rude placards at a what organisers called a "Carnival of Resistance" in Trafalgar Square while Mrs May was in talks with the president a short distance away in Downing Street.

There was a festival atmosphere at the rally.

Among Britons, Trump is one of the best-known but least-liked foreign leaders. Just 21 per cdnt of people surveyed by YouGov had a "positive opinion" of him. Among women, that figure shrank to 14 per cent.

The tone at the protest was set by a large statue of Trump sitting on a golden lavatory with his trousers around his ankles, while the placards read: "Trump stay out! We are quite capable of cocking up our own politics", "You can't come over racism" and "Lock him in the tower".

"Trump is an ignorant, 70-year-old man who has lived a life of privilege," said Anna Fenton, 23, a marketing manager from London carrying a sign reading "Ugh, where do I even start?"

Ms Fenton said she was protesting to show solidarity with "people that Trump's language and policies have harmed," including women and lesbian, gay, bisexual, and transgender people.

REUTERS