George Clandon, 71, a retired plumber from Burscough, Lancashire, whose uncle, George Lawson, was an engineer on the Narwhal when it went down, said: “The Polish guys did a magnificent job finding the Narwhal, albeit with a little luck.

“As a family we are absolutely delighted they stumbled on the Narwhal. For years we had wondered where it had gone down and what happened had happened. Uncle George can really rest in peace now.”

Tamara Lo, the daughter of the Narwhal’s Captain, Lieutenant Commander Robert Burch, said: “I was two in 1940 and only have the vaguest ‘memories’ of my father – rather like short loops of film.

“So, after nearly 8 decades of knowing about the loss of the boat, the information that divers had found Narwhal made me cry. I never realised how numerous the crew was.”

Mr Clandon, Mrs Lo and other relatives of those lost on board are to meet next month as a first step towards organising a memorial visit to the spot where HMS Narwhal went down next May.

The mission would involve six Polish and two British divers going down to the wreck while the mens’ relatives cast a wreath onto the waters above from a research vessel on the surface.

There are hopes the divers may be able to affix a permanent plaque to the wreck in memory of those whose remains still lie inside.

The HMS Narwhal lies in international waters and is therefore not closed to dives, although it remains the property of the British government. Families of those who died have called for other diving teams to treat the wreck with the respect it deserves.

Mr Clandon, who himself served in the Royal Navy until 1970, said: “My uncle was an engineer and would have taken the full impact of the bomb because he was in the engine room.

“People didn’t really appreciate what he and the other sailors were doing. There was also a lot of secrecy surrounding their work as they were laying mines to stop enemy ships leaving their harbours.

“Of course it should be treated as a war grave to protect it from scavengers and memorabilia hunters.”

A Royal Navy Spokesperson said: “Any site of naval military remains, such as this one, should remain undisturbed as a mark of respect for all those who may have lost their lives on such vessels.”

The Polish Santi Diving team, armed with sophisticated sonar equipment, confirmed the location of Narwhal earlier this year while on mission to try to find the ORP Orzel (Eagle), which disappeared mysteriously while on a secret mission for the Royal Navy’s 2nd submarine flotilla in 1940.

It was no secret there was a 90-metre long vessel lying intact 140 miles off the east coast of Scotland, but no-one knew exactly whose vessel it was.

The North Sea is littered with submarine wrecks – 150 sunken German U-Boats, as well as 50 British submarines, several French ones, two Dutch and one Polish one, the long lost Eagle that Poland has been searching for over the last decade.

Tomasz Stachura, the 52-year-old CEO of Santi Diving, said: “The size of this craft – 90 metres – is a very unique point of identification. We know that German U-boats are only 65-metres long, so we were prepared for this to be either the Narwhal or the Eagle, as no other Navies reported a loss in this area and there are only a few vessels like it in the world.”

It was only analyzing the detailed 3D sonar scans that the authorities were able to confirm that it was indeed most likely the HMS Narwhal, lost in the Battle of Britain in July 1940 after being attacked by the Luftwaffe.

The submarine had left its base in Blyth Northumberland to lay mines near German-occupied Norway. But the Germans, who had cracked the Royal Navy’s secret codes, knew the Narwhal’s route and attacked it with a bomber.

It was presumed sank in July 1940. The Luftwaffe’s report said the submarine had been hit in the stern. The side-scan sonar, in fact, reveals just that.

“The sonar shows the wreck is intact, except for the damage we can see on the stern exactly in the place where the pilot reported it,” Mr. Stachura said.

The dive team continued their search for their own sub, the Eagle, without success and upon returning to Poland, contacted the Royal Navy about their find, but never heard back.

Since their discovery the Polish divers have flooded with letters and emails from as far away as Malta and India from relatives of the British seamen lost on board.

After a report was posted on the World Naval Ships Forum, Santi’s Facebook site began to overflow with messages from relatives of the lost seamen.

“We decided to try to put all these different people in touch with one another,” said Mr Stachura.

“We kept thinking, ‘what we can do for them?’ “We thought, ‘well, we are experts in diving, so we can  dive on Narwhal, perhaps take a memorial plaque and place flowers there so that all of these people they feel they can finally close their stories.’”

Diving the HMS Narwhal

In diving, any depth below 60 metres (200 feet) is considered a “deep dive” requiring with special equipment necessary to stay down longer.

The Narwhal is a diveable wreck lying 308 (94 metres) feet beneath the surface, in international waters.

The Santi dive team are masters of deep diving on wrecks in the frigid conditions of the Baltic Sea. They were the first divers to explore the lost Nazi aircraft carrier the Graf Zeppelin, which sunk off the Polish coast in 1947.

The team use the most advanced technology available today – rebreathers, a computerized technology that mixes three gases (oxygen, helium and nitrogen) in accordance to depths and the body’s needs, while at the same time removing exhaled carbon dioxide using scrubbers, allowing the divers to stay underwater for longer. Because the diver’s breath is being recycled, the diver leaves no telltale bubble-trails  – ideal for specialized military or hard-core technical divers in scientific and commercial sectors.

The Santi dive team wear their own dry suits with heating systems and rugged JJ CCR rebreathers, the same kind used by Scandinavian military units. Each diver also carries a bailout system.

Not only is the Narwhal a very deep dive, it is also lying just 80 metres from a gas pipeline, despite  regulations requiring pipelines be at least 500 metres from wrecks.

“This makes it very complicated – the diving is very demanding, but there is a lot of paperwork necessary to get permissions, and we also need to talk to local divers in Scotland about the current,” said Mr. Stachura.

Once all permissions have been secured, the team hopes to go out to the site next May with a 20-metre research vessel, with a team made up of six Polish divers and two British divers with expert knowledge of the North Sea currents.