THERESA MAY threatened to blacklist Boeing after America put over 4,000 UK jobs at risk in a bitter trade dispute.

And the PM's Cabinet colleagues from Boris Johnson to Defence Secretary Michael Fallon waded in as the row risked turning into a fierce transatlantic spat.

4 Anglo-Canadian group Bombardier is one of Northern Ireland’s biggest employers Credit: PA:Press Association

The US Department of Commerce sparked outrage by warning it could slap a punitive 220 per cent tariff on the jets made by Anglo-Canadian group Bombardier, one of Northern Ireland’s biggest employers.

It followed a complaint by Boeing that Bombardier was benefiting from illegal state aid.

But a furious Theresa May hit back by saying she was "bitterly disappointed".

And she said Boeing's relationship with the Government was being "undermined".

In a warning to the US giant, she said: "We are very clear about the importance of Bombardier and the importance of those jobs in Northern Ireland.

"And we will be doing everything we can to ensure that we can see those jobs being guaranteed in the future."

4 Defence Secretary Sir Michael Fallon said the stunning move 'could jeopardise' Boeing’s future relationship with the Ministry of Defence Credit: PA:Press Association

Secretary Sir Michael Fallon had earlier said the stunning move “could jeopardise” Boeing’s future relationship with the Ministry of Defence, which has billions of pounds worth of existing business with the company.

At a London function, without mentioning the US by name, Trade Secretary Liam Fox branded the country "morally reprehensible".

Boris Johnson also called on President Trump to intervene.

He said: "We will be looking at what we can do to ensure free and fair trade to make sure that Bombardier gets a fair crack of the whip and first suck of the saucepan."

4 Apache attack helicopters are designed to support missions Credit: Alamy

Theresa May had already lobbied Donald Trump personally about Bombardier on the phone and in one-to-one talks.

The US action could have huge implications for the Tory’s power sharing deal with Ulster’s DUP.

Opposition leaders said the preliminary decision by the US Department of Commerce made a mockery of the pair’s so-called ‘special’ relationship.

Separately, Europhile MPs said the decision showed the folly of Brexit, given the Government has repeatedly claimed a free trade deal with the States would make up for any loss of trade with the EU.

Bombardier was due to begin delivering a blockbuster order for 125 new jets to Delta Airlines next year. Boeing didn’t even bid for the work.

But Boeing claims Bombardier’s subsidies from the UK and Canada allow them to sell airliners at below cost prices in the US and it had to speak out now. The MoD earlier this year confirmed an order for dozens of Boeing's Apache attack helicopters.

Jeremy Corbyn gave his Labour conference speech in Brighton Credit: EPA

In Brighton, Jeremy Corbyn told Labour conference: “If the special relationship means anything, it must mean that can say to Washington: that way is the wrong way.

“That’s clearly what’s needed in the case of Bombardier where thousands of jobs are now at stake.”

Lib Dem chief Vince Cable added: “We were told the UK would be at the front of the queue for a US trade deal.

"Instead, Bombardier workers risk being front of the queue for the dole.”

Union chief ‘Red’ Len McCluskey said he was optimistic a solution could be found.

The arch leftie Unite general secretary urged the British and Canadian governments to try and resolve the issue “before we get into a full blown trade war with Boeing”.

“Britain is the second biggest client in the world for Boeing. The Government has to use that leverage and say if they persist in this then they will suffer.”

4 Critics said the decision showed the folly of Brexit Credit: Alamy

Government sources said the White House was aware of the UK’s huge concerns and the sensitivities around Northern Ireland.

But Mr Fallon stormed: "This is not the behaviour we expect of Boeing and could indeed jeopardise our future relationship with Boeing."

He added: "Boeing stand to gain a lot of British defence spending.

“We have contracts in place with Boeing for new maritime patrol aircraft and for Apache attack helicopters and they will also be bidding for other defence work and this kind of behaviour clearly could jeopardise our future relationship with Boeing."

US Secretary of Commerce Wilbur Ross said: “Even our closest allies must play by the rules.”

A final decision on the tariff is due in February.