The following correction was printed in the Guardian's Corrections and clarifications column, Friday 1 May 2009

A further error has come to light in the story below about the use of seaside imagery from Northumberland in a promotional film about landlocked Alberta. The story quoted Tom Olsen, identified as "head of media relations for Canada's prime minister Stephen Harper", defending use of the foreign beach image. This led the writer to deduce, and write, that the national government was delighted with the film clip. Federal officials were not involved in the promotion, and Tom Olsen is spokesman for the premier of Alberta, Ed Stelmach.

The sea was blue, the beach was gold and the children skipping through the sand dunes seemed a testament to the healthy joys of holidays in the Canadian province of Alberta.

Tourist officials and the national government in Ottawa were delighted with the promotional clip, part of a £14m attempt to offset controversy over oil extraction in Alberta's beautiful wildlands.

But hours of sleuthing by a puzzled sailing enthusiast, aware that Alberta has no coastline, have revealed that the idyll was filmed 5,000 miles away across the Atlantic. The girl with the flying hair and her friend were romping on the sweep of sand at Beadnell Bay near Bamburgh, Northumberland, where the North Sea rolls in from Lindisfarne.

"We think it's quite funny - a landlocked province in Canada presenting an image of itself as an island," said Sheelagh Caygill of Northumberland Tourism, which is now fondly hoping to piggy-back on the international campaign. News of the gaffe is spreading like wildfire on the internet with tags such as: "Come to Alberta - no, wait, it's Britain."

The curious choice of a seaside beach for a place which has none, was spotted by Peter Bailey, a Canadian looking for places to take his dinghy. He initially thought that the scene might be set on one of Alberta's many lakes, whose sandy shores and unpolluted water are important to the tourism drive.

Oil extraction is concentrated in Alberta's Oil Sands region, which include landscapes vaguely similar to Northumberland's unspoilt coast. But Bailey tracked down the real setting - halfway between the drama of Bamburgh castle and the kipper-smoking village of Craster - after a marathon email session with the Canadian government, tourist authorities and their PR advisers.

Ottawa has responded by suggesting that the choice of Northumberland symbolised the fact that "Albertans are a worldly people". Tom Olsen, head of media relations for Canada's prime minister Stephen Harper, said: "There's no attempt to mislead here. The picture used just fitted the mood and tone of what we were trying to do."

His take that the British children were "a symbol of the future" was echoed by Olga Guthrie of Alberta's public affairs bureau, who is managing the campaign. She said: "This represents Albertans' concern for the future of the world. There's no attempt to make people think that the place pictured is Alberta."

The PR agency Calder Bateman which devised the rebranding campaign in Edmonton, Alberta's capital which stands roughly 500 miles from the Pacific and 2,000 miles from the Atlantic, said that it could not comment "because of the terms of the government's contract."

Back in Northumberland, Caygill said that local people were "actually quite thrilled" that one of their prime beauty spots was being publicised free to so many people worldwide. Legendary links between Bamburgh castle, Lancelot and Guinevere and Tristan and Isolde have been used to plug the area as perfect for romantic getaways. "We're delighted with any new way of promoting the beauty of the north of England, which is often neglected," Caygill said. "I hope that when people in Alberta realise where the beach is, they'll want to come and visit."

Beadnell was quiet yesterday, but one pre-season visitor Ian Hooper from Edinburgh sang its praises. The 52-year-old doctor said: "I'm originally from Newcastle and I love it here. I used to play in the sand dunes as a child, and now I've five children of my own and they love to play in the dunes too, and do watersports here."

The affair follows other recent outbreaks of international poaching, including the lifting of a scene from the sun-kissed Bahamas in February this year, to stand in for the Costa Brava in Spain.

More cosily, Rochdale Development Corporation was caught out using photographs of street cafes in the centre of Manchester two years ago to back its slogan that Rochdale was "a happening place".

Different worlds: Plenty of sand, but only one sea

Alberta is the size of France, Holland and Belgium but has no coast, though plenty of everything else, from deserts to icefields. Temperatures range from 40C (104F) in summer to -54C (-70C) in winter. The population of 3 million thrives on petrochemicals, exporting the world's second largest amount of natural gas. Tourist attractions include Lake Louise and the Alberta Prairies Steam Railway. The province's official bird is the great horned owl

Beadnell has a population of 528, two holiday caravan sites and a beach stretching for 1.8 miles. It hosts the largest colony of Arctic terns on mainland Britain. It has a fortified pele tower and a record of famous swimmers, including the poet Swinburne and the novelist EM Forster. Fishing continues from a port which is the only west-facing one on England's east coast. Local specialities include Craster kippers and Lindisfarne mead.

• This article was amended on Tuesday 28 April 2009. Errors of distance appeared in the story above about how seaside imagery from Northumberland was used in a promotional film about landlocked Alberta. We should have sited Edmonton about 2,000 miles from the Atlantic, not 600 miles, and about 500 miles from the Pacific, not 400 miles. The story called Alberta a province, but the headline wrongly called it a state. These errors have been corrected.