By Steve Holland and Hannah McKay
LONDON (Reuters) - U.S. President Donald Trump began a state visit to Britain on Monday but the pomp and formal banquet with Queen Elizabeth looked set to be overshadowed by his views on Brexit, the UK's next leader and a security row over China's Huawei.
Trump and his wife, Melania, will be treated to a full display of British royal pageantry during the June 3-5 visit: lunch and a formal dinner with Queen Elizabeth, tea with heir Prince Charles, and a tour of Westminster Abbey, coronation church of English monarchs for 1,000 years.
Beyond the ceremony, though, the proudly unpredictable 45th U.S. president is likely to rock the boat with the United States' closest ally, whose political establishment has been in chaos for months over Britain's departure from the European Union.
Trump has praised a more radical Brexit-supporting potential successor to Prime Minister Theresa May, and his envoys have urged a tougher British stance toward Chinese telecoms giant Huawei.
"I look forward to being a great friend to the United Kingdom, and am looking very much forward to my visit," Trump wrote on Twitter minutes before Air Force One landed.
In a sign of how he would not shy away from causing controversy on the trip, he used the same message to take a swipe at long-term opponent London Mayor Sadiq Khan, describing him as a "stone cold loser".
Britain is hoping the visit will cement the so-called special relationship between the countries and lay the platform for a post-Brexit trade deal, which Trump has said could be worked out in the near future.
On Monday, Trump will receive the full royal treatment from his hosts. After being greeted by the queen and heir-to-the-throne Prince Charles at Buckingham Palace, he will enjoy lunch with the 93-year-old monarch and other senior royals.
The queen's second son Prince Andrew will then accompany Trump to Westminster Abbey where the president will lay a wreath at the Grave of the Unknown Warrior before the day culminates with a lavish state banquet at Buckingham Palace - where men wear white tie coats with tails and women evening gowns.
UNCONVENTIONAL
But away from the pageantry, Trump is set to make his trip the most unconventional state visit in recent memory.
Trump has already waded far into Britain's turbulent domestic politics. More than a dozen candidates are vying to replace May, who announced last month she was quitting as prime minister after failing to get her EU divorce deal through parliament.
The president has repeated his backing for candidates who have said Britain must leave the bloc on the due date of Oct. 31 with or without a deal.
They include former foreign secretary Boris Johnson, whom Trump praised in an interview with the Sun newspaper on Friday, former Brexit minister Dominic Raab and interior minister Sajid Javid.
He also called for arch-Brexiteer Nigel Farage, a scourge of 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 ever happens then London will be more reliant on the United States as ties loosen with the other 27 members of the EU.
At a meeting with May, Trump will also warn Britain that security cooperation, a cornerstone of the western intelligence network, could be hurt if London allows China's Huawei a role in building parts of the 5G network, the next generation of cellular technology.
The Trump administration has told allies not to use its 5G technology and equipment because of fears it would allow China to spy on sensitive communications and data. Huawei denies it is, or could be, a vehicle for Chinese intelligence.
U.S. Secretary of State Mike Pompeo told Britain last month it needed to change its attitude toward China and Huawei, casting the world's second largest economy as a threat to the West similar to that once posed by the Soviet Union.
BLIMP
Britain's relationship with the United States is an enduring alliance, but some British voters see Trump as crude, volatile and opposed to their values on issues ranging from global warming to his treatment of women.
Hundreds of thousands protested against him during a trip last year and a blimp depicting Trump as a snarling, nappy-clad baby will fly outside Britain's parliament during the visit. Other protesters plan a "carnival of resistance" in central London.
Jeremy Corbyn, the socialist leader of Britain's opposition Labour Party, who has declined an invitation to attend the state banquet, scolded Trump for getting involved in British politics.
"President Trump’s attempt to decide who will be Britain’s next prime minister is an entirely unacceptable interference in our country’s democracy," Corbyn said.
The second day of the trip will focus on politics, including a breakfast with business leaders, talks with May in 10 Downing Street, a news conference and a dinner at the U.S. ambassador's residence.