Image copyright Reuters Image caption Michel Barnier said Airbus depended on freedom of movement for people and products

Firms such as Airbus in Flintshire face new "constraints" in moving parts and staff between its European sites, the EU's chief Brexit negotiator warned.

Michel Barnier said the UK could not have "frictionless" trade outside the single market and customs union.

He also said Britain had "more to lose" than the remaining 27 states if it crashed out of the EU without a deal.

Senior Airbus vice-president Katherine Bennett said she was confident the firm would "get over" any new restrictions.

UK ministers have said they want trade with the EU once it leaves the bloc to be as "frictionless as possible".

Mr Barnier was giving an update on Brexit on Thursday to a meeting in Brussels of the European Economic and Social Committee, an advisory group representing employers, trade unions and other interest groups.

He stressed that the EU did not want to "punish" the UK for leaving the bloc, but suggested British politicians had not "fully understood" the EU's position on free movement, the single market and its rules and regulations.

Brexit without a trade deal could result in "very cumbersome" customs procedures, Mr Barnier warned, with UK firms facing delays of days rather than hours on every export of goods to the EU.

Image copyright EPA Image caption Airbus wings are exported from Wales to assembly lines in France and Germany

He named the Airbus wings plant, which employs 6,000 at Broughton, Flintshire, as the type of operation which depended on integration with continental Europe.

It drew skilled staff from across the EU, Mr Barnier said, and relied on EU rules to ease shipments of its aircraft wings to assembly lines in France and Germany.

"Trade will never be as fluid for a country which makes the choice to leave the single market and the customs union," he warned.

Katherine Bennett, senior vice-president of Airbus, told BBC Radio 4's The World at One on Thursday the company was most worried about the prospect of restrictions on the movement of employees in high technology jobs.

But she added: "We will get over these barriers.

"We're a very integrated company and we do have people from around the world but we have a large percentage of people who are 'other EU' citizens," she said.

"It's really important that we explain to our government and of course to the European Commission about the importance of that integrated arrangement being able to continue."

In January, Airbus chief operating officer Tom Williams told MPs the company would be "entering a dangerous phase" if it could not seamlessly move people and products around the EU.

He told the Commons Treasury Select Committee that American competitors such as Boeing would be "delighted" if that happened.

However, Boeing Europe president Sir Michael Arthur later wrote to the committee pointing out it had more than 2,000 staff in the UK, which was a "critically important market, supplier base and source of technology partners" for the company.

He said Boeing was "as keen as any company for the UK and the EU to be successful in the future, giving our presence and supply chain partnerships, which we intend to continue to grow".