US President Donald Trump landed in London on Monday morning for a two-day state visit preceded by rare atmospherics that saw the visiting dignitary wading into the Conservative leadership contest, and making personal remarks about mayor Sadiq Khan.Jousting between Khan and Trump began nearly three years ago, when Washington imposed curbs on travellers from some Islamic countries. It continued during the London Bridge terror attack, when Trump flayed Khan’s handling of the response.On Sunday, Khan took it further, saying it is ‘un-British’ to be rolling out the red carpet for someone who “amplified the tweets of a British far-right racist group, denounced as fake news robust scientific evidence warning the dangers of climate change”, among other reasons.Minutes before landing at Stansted Airport, Trump took a swipe at Khan’s height, called him ‘nasty’ and ‘stone cold loser’, and reiterated his criticism of his performance as the mayor of London. He tweeted: “@SadiqKhan, who by all accounts has done a terrible job as Mayor of London, has been foolishly “nasty” to the visiting President of the United States, by far the most important ally of the United Kingdom. He is a stone cold loser who should focus on crime in London, not me......”“...Kahn reminds me very much of our very dumb and incompetent Mayor of NYC, de Blasio, who has also done a terrible job - only half his height. In any event, I look forward to being a great friend to the United Kingdom, and am looking very much forward to my visit. Landing now!”Khan responded through a spokesman: “This is much more serious than childish insults which should be beneath the President of the United States”. “Sadiq is representing the progressive values of London and our country warning that Donald Trump is the most egregious example of a growing far-right threat around the globe, which is putting at risk the basic values that have defined our liberal democracies for more than 70 years”.Demonstrations are due in central London, besides a Trump baby blimp flying overhead, as Trump meets Queen Elizabeth in Buckingham Palace for a ceremonial welcome marked by royal pomp and pageantry.Speaking ahead of the evening’s State Banquet at Buckingham Palace, Prime Minister Theresa May said: “This is a significant week for the special relationship and an opportunity to further strengthen our already close partnership”.“During his State Visit to the UK the President and I will be taking part in an historic commemoration of the D-Day landings and the sacrifice our armed forces made 75 years ago. And as we reflect on our shared history and honour those who fought so bravely on the beaches of Normandy, we also look to the future”.