British Prime Minister Theresa May is lending her government's support to Canada in a bid to resolve a potentially damaging trade dispute initiated by U.S. aerospace giant Boeing against Montreal-based rival Bombardier.

Foreign Affairs Minister Chrystia Freeland told reporters at the Liberal cabinet retreat in St. John's Tuesday that the two countries are working together on the file to protect jobs in both countries.

"We have indeed been working closely with our British allies on this issue. They have a strong interest in Bombardier and I think it absolutely makes sense for us to work in close partnership, and that's exactly what we've been doing."

Bombardier is the largest manufacturing employer in Belfast, Northern Ireland.

Canada's ambassador to Washington, David MacNaughton, said the May government volunteered to help resolve the trade complaint now being investigated by the U.S. Commerce Department.

"I think the biggest help is making Boeing realize that being unreasonable and arbitrary about this is not in their best interests. The U.K. is a big buyer of Boeing aircraft [...] and if I were Boeing, I'd be paying attention to it."

Boeing asked the U.S. Commerce Department in April to investigate whether Bombardier is dumping planes into the U.S. market, alleging government subsidies to the company allowed it to close a deal for 75 C-series passenger jets with Delta Airlines at a cut-rate price.

Global Affairs Minister Chrystia Freeland was speaking in St John's at the federal cabinet retreat 1:03

Theresa May will be in Ottawa on Monday for a state visit, when she and Prime Minister Justin Trudeau are expected to discuss the Boeing file.

MacNaughton told reporters he's asked Boeing executives to resume talks to head off the dispute. Those talks broke off in early August, when representatives of the aircraft-maker walked away from the table.

The ambassador has also reached out to U.S. Commerce Secretary Wilbur Ross, whose department is investigating Boeing's complaint.

"All we've said to Secretary Ross is that we would like to continue discussions, because we don't understand why they would be taking action on a case where [Boeing] wasn't even competing for the business. It's kind of strange."

May raised the issue last month in a call with U.S. President Donald Trump.

Canada's Ambassador in Washington David MacNaughton speaks to reporters in St John's Tuesday 1:33

Key employer in Northern Ireland

May's visit to Ottawa, while not directly linked to the Boeing-Bombardier dispute, comes at an opportune time as Canada tries to get Boeing back to the table.

Bombardier's Northern Ireland plant employs 5,000 workers directly and represents 10 per cent of the region's manufacturing jobs, where May's Conservative government holds key seats.

"These jobs are of huge importance to Northern Ireland and the economy in Northern Ireland and the prime minister wished to make that point to the president," her spokesman told reporters Tuesday, adding there had been a lot of government engagement with Boeing.

"It is in everyone's interests that we safeguard Bombardier's operations and the highly skilled workers that it has in Belfast."

A preliminary decision from the Commerce Department, which could include duties, is expected Sept. 25. A final determination is not expected until next winter.

The extent of Britain's backroom involvement became clearer on Tuesday.

High-level engagement

Officials with knowledge of the file in Washington, speaking to reporters on background, said the British have been actively flagging concerns "at all levels of the U.S. government" and directly with Boeing.

There has also been a lot of cabinet-level dialogue and co-ordination of messaging with the Canadian government, including conversations between Britain's secretary of state for business and industrial strategies and Foreign Affairs Minister Chrystia Freeland, according to the officials.

The officials said their impression is the U.S. government would prefer a negotiated settlement between Boeing and the Canadian government.

Canada's international trade minister, François-Philippe Champagne, said May understands what's at stake in the dispute for Bombardier operations in Canada and the U.K.

"It provides a lot of employment in Northern Ireland and so she has taken a similar position to us, sending a very strong signal to Boeing that they should be listening to Canada," he said.

Canada has threatened to retaliate by cancelling a lucrative order with Boeing for 18 Super Hornet fighter jets. Last week, Prime Minister Justin Trudeau raised the issue in a call with Eric Greitens, the governor of Missouri, whose state is home to many jobs manufacturing the jets.

For its part, Boeing has given no indication that it's listening to the concerns, or that it's even willing to continue talks with Canadian trade officials.