It is the sport of kings: not horse-racing, but surfing. Rare photos have emerged showing King Edward VIII, then the Prince of Wales, riding a wave in Hawaii in 1920 in what is believed to be the earliest ever picture of a British surfer – royal or otherwise.

The images were obtained from a descendant of legendary Hawaiian surfer and Olympic swimmer, Duke Kahanamoku, who gave the future king board-riding lessons off Waikiki beach. They will go on show in an exhibition at the new Museum of British Surfing in north Devon which opens on Thursday night. The new museum reveals the genteel aristocratic roots of a sport that came to be embraced by hippies and punks in the spirit of counter-culture and rebellion in the 1960s and 1970s and is now enjoyed by up to 500,000 regular surfers in the UK.

The grainy black and white shots have never been seen before outside Hawaii and show the Prince of Wales gliding down the face of a wave, arms akimbo and using an unorthodox, but apparently effective, feet-together stance. The future king, who would later abdicate to marry Wallis Simpson, was on a private, three-day surfing trip to the Pacific Ocean island with Earl Mountbatten, also pictured in the water, although the future admiral of the fleet struggled to get to his feet.

"The earliest photo so far of a Briton standing on a wave is Edward, Prince of Wales," said Peter Robinson, the founder of the museum in Braunton, who acquired the images last year from Duke Kahanamoku's grand niece. "He had gone to Hawaii in April 1920 on HMS Renown and was taken out by Duke Kahanamoku on an outrigger canoe. He had a surf lesson and did OK, but absolutely loved it. He later ordered the royal yacht to go back to Hawaii so he could surf for three days. Duke was out of the country when he returned so David Kahanamoku took him out and these pictures were taken then."

According to an interview with David Kahanamoku published in a Hawaiian canoe club newsletter in 1950, the two young royals were keen. They surfed for two hours every morning and three hours every afternoon during their July stay.

"The prince learned quickly to ride the board standing, although he did have some spills," Kahanamoku told the newsletter, adding: "Louis Mountbatten never mastered the art but was content to lie prone."

The pictures of the earliest origins of British surfing emerged as the sport in Britain reaches new heights of popularity. South West Tourism estimates that surfing is worth around £100m a year to Devon and Cornwall alone and surfing industry sources estimate that half a million holidaymakers every year try the sport for the first time while the same number again are regular surfers.

At the highest level professional British surfers are also starting to win international recognition, in particular for big wave riding. Croyde surfer Andrew Cotton, 35, was last month nominated against surfers from America and Australia for the international Billabong XXL ride of the year award for a 50ft-plus wave he caught off Mullaghmore Head, on the north-west coast of Ireland. This Easter weekend surf schools and watersports shops around the UK are bracing themselves for another influx of novice surfers, pulling on unwieldy wetsuits and braving water temperatures of less than 10C as they get their first taste of Britain's distinctive surf culture.

The new Museum of British Surfing reveals the sport was originally an upper-class pastime in the UK that only took on its adrenalin-fuelled, macho image after the arrival on British beaches of US and Australian servicemen during the second world war, and the advent of beach lifeguards in the late 1950s.

"It was a genteel, stately exercise activity, mainly of belly-boarding," said Robinson. "Wealthy holidaymakers from London or the home counties would come down for a spot of surf-riding in the morning, have cucumber sandwiches for lunch and play croquet in the afternoon."

Agatha Christie was an early exponent of the sport who learned to surf on a trip to Honolulu and wrote in her memoirs: "Nothing like that rushing through the water at what seemed to you a speed of about 200 miles an hour; all the way in from the far distant raft, until you arrived, gently slowing down, on the beach, and foundered among the soft flowing waves."

King Edward VIII, then the Prince of Wales, riding a wave in Hawaii in 1920. Photograph: Museum of British Surfing

The early equipment was rudimentary. In 1919, Tom Tremewan, an undertaker from Perranporth on the north Cornish coast, started marketing coffin lids as surfboards. Boards in the exhibition from the 1950s look more like pieces of ship work, held together with shiny brass screws instead of today's aquadynamic fibreglass. Wetsuits were homemade, and woollen sweaters were used to try and keep warm in the water.

The English aristocrats weren't the first Britons to become fascinated by the simple pleasure of being propelled to shore by the power of a wave. The exhibition features extracts from Captain Cook's 1779 journal as he described Hawaiian "natives" paddling out with their boards.

"It was a blast," recalled Kevin Cook, 61, a museum trustee who started surfing in Woolacombe in 1968. "It was young guys down at the beach. All the lifeguards started talking with Australian accents even if they were from round here. Now people are starting to appreciate that on its day north Devon has waves that stand up to anything in the world, although it is not there every day, the water is cold and it is a pain getting into a thick wetsuit."

Many British surfers agree that conditions can be tough. Occupational hazards include "ice-cream headache" from the frigid waters, waves battered out of shape by gales, and long drives to get to the most reliable spots.

Wave data shows that the growth in British surfing is more than a triumph of hope over reality. Surf forecasting company Magic Seaweed, calculates that swells averaging 10ft reach Newquay in Cornwall 58% of the time, more than at Sydney where the ratio is 44%, although a third of Newquay surfing days are marked by strong wind, compared to 10% in Sydney. Neither bear much comparison with southern California, spiritual home of the Beach Boys, where surfers are blessed with 6ft waves 80% of the time and hardly any strong winds. But the allure of British waves is growing for all generations.

On Saunton Sands in Devon this week, teachers Misa and Fearghal Magee had brought their six-month-old baby Perrin down to the beach while they took it in turns for a late afternoon surf in clean swell.

"We moved from Ireland to be close to these waves," said Fearghal. "It was the main reason. We know lots of couples who have moved down here to surf."

So, does British surfing deserve a better reputation? "I don't think we want the rest of the world finding out just how good it is."