In the Tuesday memo, the U.S. Embassy in London alerted citizens to the "numerous demonstrations" that could "attract large crowds" that may be less than agreeable toward Americans.
A statement on the United States embassy website warns U.S. citizens to "be aware of your surroundings [and] exercise caution if unexpectedly in the vicinity of large gatherings that may become violent".
Protests are expected at every stop Trump makes along the way, including a caricature blimp of him as a baby holding a smartphone flown near Parliament on Friday. "Britain is going to have to look right around the world for allies with which to do trade deals".More news: Apple patches iOS bug that crashed apps due to Taiwanese flag emoji
Trump will spend Thursday night in London at Winfield House, the official residence of U.S. Ambassador to Britain Robert "Woody" Johnson.
As well as in London, protests are expected to take place in Bristol, Newcastle, Leeds, Cambridge and Cardiff after Trump arrives here on Thursday.
Trump also shrugged off mass protests planned in Britain against his visit starting later Thursday and called the country "a pretty hot spot" over the cabinet resignations.
On Friday evening, Trump and the First Lady whisk up to Scotland for a weekend of golf and relaxation - and more protests outside his resort. That led roughly 500,000 people to sign a petition calling for Trump to be banned from entering the Britain.More news: Belgium favored in third-place match over England
The trip coincides with a tumultuous week for May after two senior ministers resigned in protest at her plans for trade with the European Union after Britain leaves next March.
Ignoring all diplomatic niceties, the convention-shredding USA president set up the four-day visit with a rebuke of his beleaguered host as she battles to stop her government falling apart over Brexit.
The state visit was never actually scheduled - there has been fierce opposition to it in many quarters of Britain - and this trip is part of a working visit instead, meaning among other things that Mr. Trump will overnight at Winfield House, the US ambassador's handsome residence near Regents Park, rather than at Buckingham Palace or Windsor Castle as a guest of the queen. She said they will discuss security and defense, an aspect of the relationship that is causing anxiety for some British politicians.
On Friday, May and Trump will hold talks on Brexit, relations with Russian Federation and trade ties at the prime minister's Chequers country residence followed by a press conference. Later, Trump will go to Windsor Castle for tea with 92-year-old Queen Elizabeth.More news: France out to rectify Euro 2016 mistakes in final, says Pogba