A grey metal box in the North Wales countryside is home to the jewel of Britain’s aerospace industry.

Airbus’s factory in Broughton, Flintshire, is where the pan-European aerospace and defence group manufactures all the wings for its commercial aircraft. The well-paid jobs, cutting-edge technology and headline-grabbing products are highly prized – by Britain, and by other Airbus factories around Europe.

Airbus has long fought off green-eyed advances from its plants in Toulouse, Hamburg and elsewhere, which are keen to wrest wing production from Britain’s clutches. But there are concerns that the vote to leave the European Union has weakened Britain’s grip on this precious gem.

High-tech manufacturers such as Dyson have dismissed concerns that extra tariffs and possible delays at borders after Brexit will hinder trade.

That may be true for independent businesses but less so for foreign-owned companies that are part of supply chains across the EU, from the car industry to pharmaceuticals, plastics and, crucially, aerospace where politics plays such an important role.

Britain has maintained its slice of the Airbus pie as long as it has been a large net contributor to the EU budget. Without that leverage, there must be a question mark over future investment.

Paul Everitt, the chief executive of ADS, the trade body for the aerospace, defence, security and space sectors, said: “We are concerned that there could be a long-term erosion of Britain’s competitiveness and that big projects will not be allocated to the UK. We are currently a big player in the aerospace industry.”

Everitt is not alone. Senior Airbus executives have warned that erecting barriers to the free movement of parts and people across its European sites may cause lasting damage to Britain’s aerospace industry.

Airbus spends about £4bn a year with suppliers in the UK – a significant contribution to Britain’s aerospace industry, which supports about 110,000 high-value, highly skilled jobs. The group employs 15,000 people directly in the UK. About 4,000 of these design the wings for Airbus planes at Filton, Bristol; a further 6,000 workers build more than 1,000 wings each year at Broughton.

The Welsh factory is where aviation classics, such as De Havilland’s Comet and Mosquito, were produced. These days, it is responsible for assembling the wings for all Airbus civil aircraft, including the new-generation A350 XWB (extra wide body).

The enormous plant receives millions of components each year from other Airbus factories and suppliers around Europe. Once the wings are built, these complex, giant structures are delivered to final assembly lines in various ways, including by road and on the Airbus Beluga super transporter aircraft.

Wings for the A380 are sent by road and sea for final aircraft assembly in Toulouse. At present, there are no restrictions or tariffs on the movement of these parts or on the people who oversee this fiendishly complicated jigsaw.

Everitt noted: “As an industry, we run a complex set of manufacturing processes in which millions of components need to pitch up from Toulouse at the right time and in the right order. [Brexit] implies significant cost … The concern is that the UK becomes less competitive because there are extra costs with moving people and components around.”

He noted that aerospace was a capital-intensive, long-cycle industry, so there were unlikely to be dramatic changes on day one of Britain’s exit from the EU.

Last month, Katherine Bennett, the head of Airbus UK, wrote in Bristol’s Western Daily Press: “We can’t shy away from the fact that future investments made by Airbus will inevitably depend on the economic environment in which we operate. The company’s business model is based on our ability to move products, people and ideas around Europe free from restrictions.”

Bennett’s comment hints at the internal dialogue at Airbus – that Brexit may hand a crucial advantage to sites in Toulouse and Hamburg, which want to grab future wing work from Britain. Even before the vote to leave the EU, well-placed sources said there was constant lobbying from the French and Germans to prise wing manufacturing away from Britain.

A senior industry source said: “It’s a constant and transparent pressure. They have always argued for that work. The next plane that comes out, I would be very surprised if the UK got much work on it. The numbers will be difficult for the UK [because of Brexit]. The question asked will be ‘why should [new aircraft projects] come to the UK?’”

What about the expertise of the engineers at Filton and Broughton? The source reckons 10% of the commercial aviation workforce – about 1,000 key engineers [800 at Filton and just 200 at Broughton] – “make the difference”. “Everything else is a commodity; everything else is up for grabs,” he said.

“For future products, as the business grows, the company will have to progressively globalise its business. I think they will offer what they do in the UK, which is cutting-edge wing design, to other companies for them to manufacture.”

A Brexit-inspired shift in wing production would not only be a huge blow to Broughton, it would be likely to trigger an exodus of suppliers. Worryingly, GKN, an engineering group that supplies the aerospace industry, last month said it would be forced to follow Airbus if it shuffled work from Britain to other sites in Europe.

Kevin Cummings, chief executive of GKN’s aerospace business, said the FTSE 100 engineering group would have to move its emphasis to where its customers were. “We are also just as much European as we are a UK company,” Cummings added.

Despite this, insiders reckon the Broughton plant should be secure for another 20 years, because it produces wings for the bestselling short-haul A320 and the mid-range A350 aircraft. But there is a growing acknowledgement that new models could be built elsewhere, unless Brexit can deliver “frictionless trade”.

Another source with knowledge of Airbus said: “Airbus is looking to make big decisions over the next two to five years. So the government needs to do what it did for the A320 and chuck in a big sum of money [to secure work for the next model].”

If the competitiveness of British sites is threatened, there is likely to be a long-term detrimental effect on Airbus’s future in the UK. “A rejection of the EU by the UK is perceived by many people in Airbus as a rejection of the values that underpin Airbus,” said the source.

“It would be foolish for Airbus to take work out and shut Broughton. But it doesn’t want to give the Europeans an excuse to marginalise the UK, and Brexit gives them an excuse.”