She resembles an old tub but the innocuous-looking Blgen held a deadly secret. Like the sirens of Greek mythology, the ship lured British sailors to their deaths.

To unsuspecting eyes, she appeared to be a cargo vessel with a bumbling crew. But hidden beneath her decks were powerful machineguns.

As soon as British submarines got close enough, the guns would open fire.

Today this piece of floating history - believed to be the only one left in the world - is a luxury floating home and up for sale with a price tag of £195,000.

Owner Tim Burman said: "She is unique and just the most extraordinary bit of kit."

Built by the Germans in 1940, the 'Q' ship was deliberately designed as a decoy and made to look like a cargo ship or sometimes a lifeboat.

Tim, who now berths the boat in Brighton Marina, said: "They were basically bait. They were built to look about 30 years old so that anyone coming across one wouldn't pay much attention.

"They had two crews - a 'panic' crew - who would appear like a bunch of amateurs, maybe a chef or a captain with a cat and a parrot in a cage - and a battle crew. They would lure the submarines in close and at the last moment drop the hatches and give them hell."

Tim believes the Germans purpose-built five 'Q' boats and converted another ten vessels for the same job.

His boat, originally called the Karl Fitzpatrick, was never used as anything other than a spy trawler.

In her last chase, she fled to the Faroe Islands, where she was abandoned. Stripped of her fittings, she eventually sank.

In 1953, after two years under the water, the Danes reclaimed her and renamed her the Blgen - which means 'wave in the sea'. They set her to work 'tramping', carrying furniture and pianos on canals.

She carried cargo between the Baltic and the North Sea until 1973 and was then taken to a new home on the Isle of Wight, where she suffered a fire and another sinking.

When Tim found her in 1998 she was in a sorry state and he intended to sell her for scrap.

"But she was still so strong and made of pre-nuclear steel - a 14mm thick armour plate. Cutting her up was also more expensive than putting her back together. So, I decided to restore her and that has turned into a five-year labour of love."

Now everything on the Blgen is shipshape and Bristol fashion. The ship is about half the size of a Dutch barge but, thanks to Tim's careful planning, has the same living space as a three-bedroom house.

The three cabins can sleep eight. The captain's quarters has a scaled-down four-poster bed with a mirrored ceiling. There are three bathrooms, two full-size baths, lounge, saloon and office area.

Tim, 35, is a shipwright and carpenter and makes his living doing up and selling on boats, bikes and chandlery. He shares his floating home with two canine crew members, Sam and Ruffles.

He said: "Sam - also known as Fatboy - has travelled more than 2,000 sea miles and Ruffles has done about 800. They are real sea dogs."

The ship also has an uninvited crew member on board - a ghost.

Tim said: "It is a black man wearing a red neckerchief. There are two theories - either that he may have been a German with his face blacked to further add to the confusion because no one would be expecting a black guy. Or it could have been a stoker covered in grease or soot. I have never seen him but I have heard him walking up the starboard side of the ship, on to the bridge and slamming the door, even when it is shut."

The ship has welcomed one famous visitor on board - round-the-world yachtswoman Ellen MacArthur. But Tim has not yet managed to find anyone, or a descendent of anyone, who served on the Karl Fitzpatrick.

He is however, used to dealing with inquisitive stares and questions from strangers.

He said: "It is great fun living on a piece of history. It's an alternative home and I absolutely love it. But now it is finished it is time to move on."

Anyone interested in buying the Blgen can contact Tim on 07770 790180.