THERESA May’s US visit has been branded a “terrible mistake” by Sir Vince Cable, the former Business Secretary, who suggested it was done out of desperation to prepare the ground for a transatlantic trade deal post Brexit.

Ahead of the Prime Minister’s arrival at the White House, the leading Liberal Democrat said: “I fear the main motive was desperation…to get some kind of bilateral agreement out of the Brexit negotiation. It was a terrible mistake to have gone rushing off to Trump like that.”

Accusing May of “getting into bed” with the Trump team, Sir Vince told the RT television channel, which is funded by the Russian Government, there was “a great danger of endorsing the Trump approach to the world, which is economic nationalism, protectionism, all the things that the British government is totally opposed to”.

Earlier, Ed Miliband, the former Labour leader, also decried Mrs May’s visit, stressing how the PM had made a "mistake" in aligning herself so closely with Donald Trump.

He said the PM's hopes of securing an early trade deal with the new US administration was a "dangerous Trojan horse," which could erode important UK regulation on healthcare, climate change and workers' rights.

Mr Miliband contrasted her approach unfavourably with that taken by Angela Merkel, the German Chancellor, in the wake of Mr Trump's election victory.

"Think of what Angela Merkel did the day after the US presidential election. She said: 'Yes, a partnership with America is important but on the basis of certain norms and values, of human rights, of commitments to equality, things that are important.’"

Ahead of her press conference and bilateral talks with the President, Mrs May and Mr Trump posed somewhat stiltedly for photographs at the bust of Sir Winston Churchill, which he had restored to the Oval Office after it was removed by Barack Obama.

Standing alongside the PM with cameras clicking furiously he pointed to the bust and said: "This is the original. It's a great honour to have Winston Churchill back."

A smiling Mrs May responded: "Thank you, we were very pleased that you accepted it back."

Earlier, the PM paid her respects to the military dead of the US at Arlington National Cemetery.

She laid a wreath at the Tomb of the Unknowns at the Virginia cemetery, which holds the remains of unidentified US troops from the First and Second World Wars, as well as the Korean conflict.

Dressed in sombre black, Mrs May was greeted by troops representing all military units based in Washington, led by Major General Bradley Becker, commander of Joint Force Headquarters for the national capital region.

A cannon was fired 19 times as the PM's convoy arrived at the cemetery and made its way to the memorial, which stands on a small hill looking down over serried ranks of gravestones to the monuments of Washington a few miles away across the Potomac River.

After a military band played the national anthems of the UK and US, Mrs May mounted the steps to lay a wreath of red poppies, bowing her head in respect as a single trumpeter sounded the Last Post.

More than 400,000 US troops killed in conflicts from the Civil War to the ongoing War on Terror are laid to rest at Arlington.

Among them are a number of British troops who died fighting alongside US forces.

Also at the cemetery are a memorial to the victims of the Lockerbie terror attack and the grave of assassinated US president John F Kennedy.

The PM also laid a wreath at the grave of Sir John Dill, the Field Marshal sent to Washington as Churchill's personal representative during the Second World War.