Sadiq Khan has urged Theresa May to stand up to Donald Trump, as he accused the US president of "playground" behaviour.
The London mayor, who was the subject of an insult in a tweet sent by Mr Trump minutes before he landed for his UK state visit, also defended Jeremy Corbyn's decision to boycott a dinner hosted by the Queen for the American leader.
Mr Khan said he believes Mr Trump has become a "poster boy" for the far-right.
Mr Trump branded the Labour mayor a "stone cold loser" in a two-part tweet as he touched down in Britain on Monday.
Asked how it felt to be described in such a way, Mr Khan said:
Mr Khan said he hoped the Prime Minister would challenge Mr Trump on some of his more controversial behaviour as president, including language around women and minorities and views on climate change.
Speaking to reporters at Downing Street Donald Trump said:
