The US President Donald Trump is set to travel to the UK today following his meetings with world leaders at the NATO summit in Brussels.
Tight security is in place, with huge demonstrations expected against his visit.
British police have said the security operation surrounding his visit will be the largest mobilisation since the London riots in 2011.
Thousands of officers from nearly every force will be on duty for the trip.
The security operation is expected to cost between £8m and £10m (€9.05m and €11.3m) and will put police under "unquestionable pressure."
UK Police Federation chairman Simon Kempton said operations were likely to become "merely reactive" during the visit.
Police specialists from firearms, public order, traffic and special escort teams will all be involved in making sure the controversial trip goes smoothly.
The Trump Baby Blimp is inflated during a practice test, at Bingfield Park in north London, 10-07-2018. Image: Kirsty O'Connor/PA Wire/PA Images
President Trump is expected to avoid central London, where the bulk of protests will take place, instead visiting Blenheim Palace, Chequers, and Windsor Castle.
He will be the guest of honour this evening at a dinner hosted by British Prime Minister Theresa May this evening.
Tomorrow, he will have tea with Queen Elizabeth at Windsor Castle.
He has spent the last two days at the NATO summit in Brussels, where he suggested the UK is in turmoil over “Brexit” and declared Germany a "captive" of Russia.
Britain’s Brexit Secretary David Davis and Foreign Secretary Boris Johnson both resigned in recent days over the Government’s latest Brexit proposals.
President Trump said it was "up to the people" whether Theresa May remains as UK Prime Minister and suggested he would make time to visit his "friend," Mr Johnson.
He also called on NATO members to increase their defence spending to 4% of GDP – double the current goal.
He is set to travel between UK locations in his bulletproof "Beast" limousine, surrounded by dozens of police and security service vehicles.
He will spend the weekend on a private visit to Scotland where he owns two golf courses.