Americans in London are being warned to keep a low profile during President Donald Trump’s visit later this week in case protests against him turn violent.
The US Embassy in London issued the alert ahead of Trump’s arrival on Thursday after attending a NATO summit.
Thousands of protesters are expected to join demonstrations during his visit, including plans to fly a blimp over parliament portraying Trump as an angry orange baby.
Nearly every police force in England and Wales has contributed to cover the event - the biggest mobilisation since the 2011 riots - consisting of thousands of officers. Chairman of the Metropolitan Police Federation Ken Marsh said the operation is expected to cost between £8m and £10m.
While Britain regards the United States as its closest ally, Trump’s comments on militant attacks in Britain and his retweeting of anti-Muslim videos posted by a leader of a far-right UK group have sparked anger.
More than 50,000 people have signed up to demonstrate in London on Friday against his visit, although a counter-gathering to welcome him is also planned.
“Numerous demonstrations are being planned for July 12 to 14, 2018, surrounding the visit of the President of the United States to the United Kingdom,” the US embassy said in the alert on its website.
“Several of the events are expected to attract large crowds and there will be road closures in connection with those events.”
Its advice to US citizens was to “keep a low profile” and “exercise caution if unexpectedly in the vicinity of large gatherings that may become violent”.
Trump arrives in Britain on Thursday after the NATO summit in Belgium and will stay overnight at the central London residence of the US ambassador, where a high metal security fence has been erected outside.
He will hold talks with Prime Minister Theresa May, meet the Queen at Windsor Castle and attend a black tie dinner at the home of former World War Two leader Winston Churchill - all outside London.
The President is also due to travel to Scotland, where he owns two golf courses and Scotland’s interim police chief has said more than 5,000 officers would be needed for to cover the trip, including specialist riot and armed units.
Ahead of his visit, Trump said Britain was “in somewhat turmoil” as the PM grappled with a political crisis.
Senior cabinet ministers David Davis and Boris Johnson quit this week over her plans for trade ties with the European Union after Britain leaves the bloc next March.
“I have NATO, I have the UK, which is in somewhat turmoil, and I have (Vladimir Putin),” Trump said as he set off on his trip to Europe which includes a meeting with the Russian President in the Finnish capital Helsinki.
“Frankly, Putin may be the easiest of them all. Who would think?”
Relations between Britain and Russia are at a post-Cold War low since May blamed the Kremlin for the poisoning of former Russian agent Sergei Skripal with a Soviet-era military nerve agent in March.