What's wrong with his claims:
Another theory: Many British press outlets, like The Telegraph, have speculated that Trump is unhappy that his planned visit to the U.K. was downgraded from a "state visit" to a "working visit" after his controversial comments regarding terrorist attacks in London and Manchester last year. That meant that his trip would not feature many of the most prominent "bells and whistles," like an official visit to meet Queen Elizabeth II via a carriage ride parade.
The reaction from Downing Street: "The U.S. is one of our oldest and most valued allies. We have a strong and deep partnership that will endure.”
London Mayor Sadiq Khan:
Former Labour Party leader Ed Miliband:
Some on the right sided with Trump like Foreign Secretary Boris Johnson, though a Downing Street spokesperson refused to say whether Johnson was speaking in an official capacity for Theresa May's government:
Former UKIP leader and Trump pal Nigel Farage also backed Trump on BBC Radio 4: “It is disappointing. He has been to countries all over the world and yet he has not been to the one with whom he is closest. I would say it is disappointing. Maybe, just maybe, Sadiq Khan, Jeremy Corbyn and the Labour Party planning mass protests, maybe those optics he didn’t like the look of.”