Relations between Belgium and the Netherlands are generally warm, with the neighbouring states sharing a navy and even, in part, a language. But decidedly unflattering comments about the Belgian coastline by the Natuurmonumenten, the Dutch version of the National Trust, have proven to be the cause of some irritation on the Belgian side of the border – and perhaps also a little self-reflection.

“The Flemish coast is a disaster. It’s one giant boulevard. That’s why all those Belgians are coming here,” Bjørn van den Boom, head of public affairs at the state-sponsored conservation organisation, told the daily newspaper De Volkskrant.

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Van den Boom was speaking in the wake of new figures showing a record number of tourists coming to the Netherlands – some 17.6 million last year – including an 11% year-on-year rise in visitors arriving to enjoy the unspoilt Dutch coast.

On the wide sandy beach of Knokke-Heist, an upmarket Belgian town famous as a destination for artists hoping to catch the “special light over the sands”, the analysis fell rather flat. “What have the Dutch got? There’s nothing there,” said Alexander Descamps, 71, enjoying a walk in the sun with his daughter, grandchildren and dogs. “Look, my dogs are loving it. The Dutch have got nothing.” In the town’s tourism office, across the road from a towering wall of apartment blocks facing down over the beach and the sea, one man spat: “Who the fuck said that? All the rich Dutch come here.”

Anthony Wittesaele, the alderman responsible for the town’s 12km strip of coast near the Netherlands border, played his country’s trump card. “I don’t know how many Belgians go to Holland because they are not really known for their good food or their savoir vivre,” he mused. “It is true that their coastline is nature foremost, and a few seaside resorts are a bit like Brighton in England – I mean old and stuck in time – that’s maybe attractive for Belgians … But, I don’t think a lot of Belgians go there. I don’t see too many Belgian cars.”

Behind the bluster the truth is that Belgians have long been dissatisfied with the state of their 65km of coastline. A policy in the 1960s of trying to guarantee every citizen the chance of a place on the seafront has led to what local people describe as an Atlantic wall of apartment blocks, some 30 storeys high, looming down over the beaches. In the Netherlands, in contrast, a coastal pact was recently signed between more than 60 developers, local authorities and conservation organisations to ban extra building on unspoiled land. The result has been a sprucing up of the old holiday resorts and the protection of the sands and nature reserves that first attracted visitors.

“There might be some truth in what they say,” conceded Wittesaele. “The Atlantic wall, as we call it, sits in front of apartments looking over the sea and it isn’t very attractive. But we have had certain towns across our coast that are exceptions. De Haan [for example] with the small white villas in the dunes. There are places where it is more visually attractive.”

Our clientele is the old rich families, the richest Dutch people, German people, and some of the richest French

He said of Knokke-Heist: “Since the end of the 19th century we are a resort that is a bit special: the Monaco of the Belgian coast. The artists have been coming for 150 years. There are 80 galleries, a world record in the number of Michelin-starred restaurants. Premium real estate is above Paris per square metre, and just below London. Our clientele is the old rich families, the new rich families but also the richest Dutch people, German people, and some of the richest French.”

Van den Boom is unrepentant, unstirred by Knokke-Heist’s affluence. “I have a lot of Flemish friends. Belgians are divided on almost every topic but on this one they agree: they despise their coastline,” he told the Observer. “It is dreadful, actually. I’m sorry to say so, but I have never met a Belgian who doesn’t agree with me. There is no quality landscape any more. That’s a consequence of the government not planning and managing how they want to build their coastline.”