Fans of British fare in France have suffered an unsavoury Brexit shock -- grocery retailer Marks and Spencer hasn't been able to stock its popular sandwiches and meals since Britain's official exit from the EU on January 1.

Hungry shoppers found empty shelves this week at more than a dozen M&S Food stores in and around Paris, depriving them of club sandwiches, pork pies and ready-to-eat curries, popular in particular with harried lunch crowds.

Instead, signs in French and English apologised that "Due to new UK/EU import legislation, we're sorry some of your favourites might be missing. We're working hard to get them back soon."

"It's amazing, I come here to buy stuff to eat but there's nothing," said Ludovic Bonnet, a marketing director, at the M&S in an ornate gallery right opposite the fabled Grevin wax museum.

"It's linked to Brexit I suppose -- they wanted to leave, now they have to live with it," he said.

The shortage brought home for many the fact that despite pledges on both sides of the Channel to maintain a smooth flow of goods, the new customs systems have disrupted decades of frictionless trade.

"I came especially for their broccoli and spinach," said Sarah, who said she works in sales.

"Does this mean they're going to close? That would be a shame, I really like their products," she said.

M&S chairman Archie Norman had warned as far back as August 2018 of this particular Brexit risk.

"If our lorries are sitting in a lorry park near Dover for half a day, that would be the demise of the great M&S sandwich in Paris," he told The Financial Times.

The sandwiches and other meals for the retailer's 21 food stores in the country -- all in Paris, one in the northern city of Lille -- are made in a factory in central England.

Norman suggested that setting up production in France was not a viable proposition.

An M&S spokesman said in a statement that "As we are transitioning to the new processes, it is taking a little longer for some of our products to reach stores."

"But we are working with our partners, suppliers and relevant government agencies and local authorities to quickly improve this."

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MARKS AND SPENCER GROUP