Brexiteers are “not telling the truth” when they claim France would not need to impose onerous and costly border checks on imports of UK produce in the event of a no-deal Brexit, the President of the Normandy region has said.

Some Brexiteers have argued that because the UK and the EU are currently fully aligned in terms of food and plant standards it would be unnecessary for France to check UK produce entering the EU after 29 March 2019, even though Britain would suddenly be a “third country”.

And some have even sought to argue that the imposition of such checks would be illegal under World Trade Organisation rules.

Lord Lilley, a pro-Brexit former UK trade and industry secretary, suggested this in an interview with the BBC’s Today programme on Monday, as he sought to play down the economic risks of leaving the EU without an agreement.

But Hervé Morin, President of the Normandy region and a former defence minister in the cabinet of President Nicolas Sarkozy, insisted on Wednesday that such checks would be unavoidable due to EU customs union and single market rules.

“The British are sovereign, but it’s the European rules we apply in France,” he told The Independent, speaking at the French ambassador’s residence in Kensington, central London.

“It’s a decision that stems from the EU. We are bound by European rules – as are the Dutch, the Belgians and the Irish.”

“Anybody who says something different is not telling the truth.”

The prospects of such checks is deeply worrying for UK for UK farmers.

The National Farmers Union president Minette Batters said in September that crashing out of the EU would be an “Armageddon scenario” for British farmers.

Trade experts agree with the reading of Mr Morin and dismiss the claim that WTO rules forbid new checks.

“The EU is obliged by the WTO to treat the UK as it treats other third countries. That is, with many more frictions than the UK faces at present as a member of the EU,” says Alan Winters of the UK Trade Policy Observatory.

What does a no-deal Brexit mean?

Normandy is home to a number of major ports, including Cherbourg, Le Havre and Caen, serving both the tourist and business trade.

Mr Morin said that there were “huge challenges” to get the infrastructure in place for future customs checks, even assuming the UK enters a 21-month transition period in March 2019.

“There’s a lot of stake economically,” said Mr Morin. “Customs will have to be set up, capacity will have to be increased.”