Any day now the dwindling colony of Black-headed Gulls nesting on the Copeland Islands, off Northern Ireland’s east coast, will receive an unwelcome visitor as thieves arrive to rob their valuable eggs.

But this year the police will be waiting for them as they attempt to stop the illegal sale of the eggs to some of the country’s top restaurants.

The short season during which gulls’ eggs are on the menu in London gentlemen’s clubs and the capital’s fashionable restaurants is in full swing. “The Black-headed Gull’s egg is a thing of joy and beauty,” says Fergus Henderson, chef at the St John bar and restaurant in Smithfield.

Marco Pierre White has extolled the virtues of gulls’ eggs in his television series Marco’s Great British Feast. Every year Natural England, the countryside and management agency, grants special licences to just 26 people to harvest gulls’ eggs from six specific sites.

A traditional food before the Protection of Birds Act was introduced in 1954, forbidding the taking of their eggs from the wild, the eggs are a culinary novelty at this time of year. They sell for around £6 each.

But the practice is controversial and, in the case of the Copelands colony, potentially fatal.

Inhabited until the 1950s, the Copelands are internationally recognised as an important breeding centre for seabirds, but this pristine wild environment, just off the North Down coast at Donaghadee, is under attack from robbers. “The colony has collapsed in the last five years,” said Neville McKee, a scientist long fascinated by the islands.

Professional criminals are stealing them from legally protected but, because of their remoteness, vulnerable locations around the British Isles where the birds seek isolation to raise their chicks. The Copelands is just one, if not the most extreme example.

Volunteers from the Copeland Bird Observatory and the Royal Society for the Protection of Birds have counted just 200 pairs of Black-headed Gulls arriving this year to nest — fewer than a quarter of the traditional colony.

“They don’t really like their eggs being stolen, they get fed up of losing them so they stop coming here,” Mr McKee said.

There are no licences granted in Northern Ireland to harvest the eggs. In recent years about 3,000 eggs have been stolen from the Copelands during the month when Black-headed Gulls are laying. But other species are also affected, including Arctic terns, which arrive in the British Isles from Antarctica to spend the summer. Mr McKee believes that their eggs are passed off as plover eggs. “In any case whoever is doing this is simply taking all the eggs they can find. They’re not making any distinctions.

“The birds lay twice and only a second time if the first attempt fails. What we’ve found is that the thieves are emptying the nests, then coming back a week later when they can be sure that there will be a fresh batch of perfect eggs to steal.”

Philip McNamara, a local boatman with an intimate knowledge of the islands, said: “The thieves just toss all the eggs out of the nests on their first visit, they don’t care what damage they do. That way when they come back a second time they are guaranteed a good collection.”

Such is the alarm at the disappearance of the gulls from the Copelands that police visited the island last week and launched a campaign, urging public vigilance. “We do believe that it’s an organised group doing this, which is then providing the eggs to restaurants,” Constable Susan Farr said.

“The theft of these protected eggs presents the very real prospect of the seabird colony on the Copeland Islands being wiped out,” Inspector Stephen Macauley said.

“I would ask the local community, particularly those in maritime activity, to be vigilant. Any suspicious activity in or around the islands should be reported to us. The penalty for anyone found guilty of the theft of protected eggs is a maximum of £5,000 per egg.”

He added: “Volunteer staff at Copeland Bird Observatory have worked tirelessly to provide a safe habitat for many different species of birds and it is devastating to see their dedicated work ruined by callous thieves who seem to have no comprehension of the damage they are inflicting.”

The Black-headed Gull has been given “amber status” by the Royal Society for the Protection of Birds because its numbers have halved over the past 20 years.

Ian West, head of investigations at the RSPB, said: “There is concern that legal trade in products of threatened species can mask the illegal trade. How does the consumer tell the difference?

“Is it appropriate that an amber-listed species of conservation concern such as the Black-headed Gull in England be subject to the legal taking of thousands of eggs a year under a special licence? It must have an impact.”

For Fergus Henderson and other chefs promoting traditional foods the prospect of a total ban on the harvesting of gulls’ eggs would be a serious blow. “It’s a very short moment, but a brilliant celebration of a British seasonal moment.

“It’s a lovely way to start lunch, a glass of champagne and a gull’s egg with celery salt. There will always be under-the-counter gulls’ eggs.”

But while Copeland’s endangered colony would certainly benefit, Neville McKee is among those who remain to be convinced that a total ban is the right course of action. “Thousands of eggs used to be harvested when the islands were inhabited. But it was done on a sustainable basis then.”

Times Recommends

• Oh no, Mr Darling: you have failed
• BBC survives dogfight over Kennel Club expose
• Where the Rosetta belongs can’t be set in stone