The U.S. has proposed imposing a 220 per cent tariff on Bombardier passenger jets following Theresa May’s decision to prioritise a ‘transition deal’ with the EU over a U.S. trade pact and rail against President Trump at the United Nations General Assembly.

The U.S. Department of Commerce ruled in favour of an interim tariff of 219.63 per cent on sales of the C-Series jet to American airline Delta after rival Boeing complained it has receivied unfair state subsidies from the UK and Canada, reports The Guardian.

“Boeing claimed that Bombardier’s C-Series aircraft, part of which is made in Belfast, are being ‘subsidised’, in part, due to a $1bn [£740m] bailout by the regional Quebec government in Canada,” it said in a statement.

The decision comes after Prime Minister Theresa May prioritised concessions to the EU over regaining powers to make international trade deals, by locking the UK into a two-year transition period beyond March 2019.

The speech announcin this decision, made in Florence, Italy, is reported to have been “pretty much dictated” by the bloc’s bureaucrats.

Farage tells Sky News he doesnt like May's line on "we dont seek unfair competitive advantage" – why he voted Brexit pic.twitter.com/KNgYe3bMJT — Faisal Islam (@faisalislam) September 22, 2017

Brexit campaigner Nigel Farage said that “the message from Florence [was] Britain is not open for business and that, for me, is the saddest part of this speech.

“What has been signalled today is we will not sign any trade deals until 2022, and that is at the most optimistic.”

U.S. President Donald Trump and his administration previously extended repeated pledges to stand by Britain during Brexit and prioritise Britain in bilateral trade deal negotiations.

President Trump even promised a “very big, very powerful” trade deal with the UK in July at his G20 meeting with Prime Minister Theresa May.

However, despite Trump extending the hand of friendship, May used her UN General Assembly speech on September 20th to lecture the president on his travel ban and the U.S. withdrawal from the Paris agreement on climate change, potentially alienating Britain’s best ally in a post-Brexit world.

"Working on major Trade Deal with the United Kingdom," announces President Trump. "Very big & exciting. JOBS!" https://t.co/q5xTGOIivC — Breitbart London (@BreitbartLondon) July 25, 2017

Reacting to the Florence speech, sources to the President allegedly told the Daily Express that the UK needs to be free to sign a trade deal with the U.S. by 2020 if it wants the guarantee of his support.

The source said the president was briefed on the Florence speech: “His concern is the UK finds a way of being able to negotiate trade deals before the elections in 2020.

“A good deal with Britain isn’t just about the special relationship that he respects so much, to him it’s also about jobs.

“If the Democrats win, it’s pretty clear they won’t be as eager as the President to bind the countries closely together, or at least, not so quickly.

“They are likely to see Brussels as the place where all the action is, and Britain will be back to the back of queue.”

The Special Relationship https://t.co/4hJobMK2zG — Breitbart London (@BreitbartLondon) September 13, 2017

A UK Government spokesman said of the U.S. Department of Commerce’s decision to raise tariffs on Wednesday: “This is a disappointing interim statement but only the first step in the process.

“As the Prime Minister said last week, we will continue to strongly defend UK interests in support of Bombardier at the very highest level because an adverse outcome risks jobs and livelihoods among the 4,200 skilled workers in Belfast.

“Boeing’s position, in this case, is unjustified and frankly not what we would expect of a long-term partner to the UK – as well as damaging the wider global aerospace industry.”

The Department of Commerce is due to make a second tariff ruling on October 5th, with the U.S. International Trade Commission making a decision to either uphold the penalty or remove it in February 2018.

It is feared that, having turned away from the U.S. in favour of an unfriendly EU, the Prime Minister will be able to do little influence the decision.