The Trump administration has announced it wants to start formal trade walks with the UK immediately after Brexit.

The US Trade Representative's office wrote to Congress yesterday to say it plans to start negotiations 'as soon as it is ready' after Brexit Day on March 29, in news that will provide a welcome boost to Theresa May.

The department will also start working on a deal with the European Union and Japan, it revealed in two other letters.

President Trump (pictured yesterday) has long said he wants a trade pact with Britain, and hailed Brexit as a 'wonderful opportunity' for a 'big and ambitious' UK-USA agreement

President Trump has long said he wants a trade pact with Britain, and hailed Brexit as a 'wonderful opportunity' for a 'big and ambitious' UK-USA agreement in a joint statement with Mrs May in New York.

The message from Robert Lighhizer, US trade representative, to Orrin Hatch, the chairman of the Senate finance committee, came in a letter on Tuesday as the UK continues with last-ditch negotiations with Brussels.

'The United States and the United Kingdom are the first and fifth largest economies in the world, respectively, and maintain a broad and deep trade and investment relationship,' Mr Lighhizer said.

'An ambitious trade agreement between our two countries could further expand this relationship by removing existing goods and services tariff and non-tariff barriers and by developing cutting edge opportunities for emerging sectors where US and UK innovators and entrepreneurs are most competitive.'

Under American trade law, the Office of the U.S. Trade Representative must tell lawmakers what it hopes to achieve at least 30 days before talks formally begin.

The news sparked a comment from the UK's director general for trade policy John Alty, who responded to a tweet querying whether his team were 'in the loop' with the negotiations by saying, 'I can assure you we are... thank you for your concern'.

It comes weeks after the US won agreement on reworking the North American Free Trade Agreement (NAFTA) with Mexico and Canada, and as the administration faces continuing trade friction with China.

The administration aims to 'address both tariff and non-tariff barriers and to achieve fairer, more balanced trade' with the EU and Japan, the letters said.

The news will come as a welcome boost to Theresa May (pictured on Monday in Vauxhall) as she is embroiled with complex last-ditch negotiations with the EU

Japan 'is an important but still too often underperforming market for U.S. exporters of goods,' the letter said. It noted the United States has a $69 billion trade deficit in goods with Japan and much of that is in the auto sector.

The letter on the EU noted the European Union and the United States have $1.1 trillion in annual two-way trade 'the largest and most complex' economic relationship in the world and added that the United States has a $151.4 billion trade deficit in goods.

In a separate development, Britain's trade minister Liam Fox will tomorrow 'categorically' deny that the government plans to lower foods standards to win trade deals after Brexit.

Mr Fox is also expected to say the UK will need a longer transition period to make a free-trade deal with the European Union, according to The Times.