The suggestion that a Royal Navy vessel containing the remains of its crew has been raised by China without the British government being informed has provoked concern in London and among the relatives of the dead.

A Foreign Office spokesman said the ministry was investigating the reports to try to confirm the fate of the vessel.

Captain Andrew Tate, Royal Navy attache to the British Embassy in Beijing, said: "Clearly if the submarine has been raised we would have expected there to have been some discussion with the United Kingdom and the Ministry of Defence and our concern would be over the bodies that still remained in the submarine."

Calls to China's State Council and the National Defence Ministry in Beijing were not returned.

Grainy photos taken from other Royal Navy ships taking part in the same manoeuvres as HMS Poseidon in 1931 show the helplessness of crews on the surface who are unable to assist their colleagues on the seabed 130ft below.

There are images of the 30 men who managed to scramble into the water before it sank being brought aboard the aircraft carrier HMS Hermes wrapped in blankets and others images showing bubbles from the submarine breaking the surface.

More than three hours after the submarine had settled on the bottom, eight men equipped with the new Davis Submerged Escape Apparatus, a rudimentary underwater breathing system, managed to leave a bow compartment. Two failed to reach the surface and another died later.

More photos from the date of the accident show the subsequent memorial service at sea for the victims and the burial of two men whose bodies were recovered.

Mr Schwankert said he began investigating the fate of the submarine after spotting a description of its salvage in a naval magazine in China.

"I first saw evidence of a salvage in very late 2005," says Schwankert. "Early on, it didn't make sense and, at the time, I didn't think it was possible or that China wouldn't have had the technology to do it.

"The material I saw was published in a magazine that could have been purchased on any news-stand. Anyone could have bought a copy," said Schwankert.

Subsequent research turned up further clues, including a passing mention of operation to recover vessel on the Shanghai Salvage Bureau website.

Schwankert believes the references in little-known sources means that no-one has previously pieced together the puzzle.

The biggest unanswered question is over the remains of the 18 crew who were unable to escape when the submarine, built by Vickers in Barrow in 1929, sank.

"It's a very good question," said Schwankert. "There would almost certainly have been the remains of the 18 crew who died aboard the Poseidon entombed within it at the time of the salvage.

"I feel sure they are buried somewhere near Weihai, but there are at present no indications where."

Schwankert, who is writing a book on his research, does not believe that HMS Poseidon was salvaged in order to learn any technological secrets that it might have contained as Chinese submarines were already based on more advanced Soviet vessels.

George Malcolmson, a historian with the Royal Navy Submarine Museum in Gosport, said: "The Chinese obviously knew where the wreck was, so they wanted to recover it for military training.

"As it was in their territorial waters, they clearly didn't feel the need to ask anyone to go ahead and do just that.

"I do not think they will see it as interfering in a war grave and they might say that they brought it up but claim that there were no remains in it."

Relatives of two men who escaped HMS Poseidon were in the city last week to attend a commemoration service, with Capt Tate reading the Submariners' Prayer aboard a vessel off the former Royal Navy base on the island of Liugong.

The relatives later tried to locate the graves of the men whose bodies were recovered but were forced to leave the colony cemetery by Chinese naval personnel.

David Clarke, an IT expert from Lancashire, attended the ceremony close to the spot where his grandfather, Petty Officer Reginald Clarke, was one of those who was in the sunken vessel for three hours before making the perilous ascent to the surface.

"He had nightmares for years afterwards, although he didn't talk about it very much, and he suffered very badly from his exertions deep underwater and the pressure.

"Technically it is a war grave, even though it was not sunk in combat, but the issue of whether it was raised is less important than the question of where the sailors' remains ended up."

Doreen Ridsdale's father, Walter Jeffery, was a Chief Petty Officer Telegraphist aboard the submarine and kept a diary of his 25-year Navy career, including the sinking of his first ship.

"He wrote in the diary that he was told to get out of his radio room and if he had not got that message then he would probably have gone down with the boat," said 77-year-olD Ridsdale, who was born in Leamington Spa but now lives in Prince Rupert, Canada.

"He wrote about the concern he felt about his shipmates as he looked at the spot where the ship had gone down, but I never remember him talking about it to me," she said. Jeffery died in 1978.

"If the Chinese did raise the submarine, what did they do with it and where are the remains of my father's shipmates?" she said. "I wouldn't like to think about how I would feel if it was my father's remains involved."