The insider said that Mr Trump is known to have an aversion to slopes or stairs, and said this could have been the reason for the president’s decision to grasp the Prime Minister’s hand.

Such a fear is a recognised condition – called bathmophobia.

As the pair walked along the White House colonnade on Friday, they encountered the top of a gentle slope. It was Mr Trump who then offered his hand to Mrs May, apparently anxious the prime minister should steady the nerves of the world’s most powerful man.