For sail: No Man's Land Fort

An historic fortress near the Isle of Wight is for sale. But who on earth will take it on, asks Kate Watson Smyth

It's billed as the ultimate island hideaway. But there is no curving stretch of golden sand dotted with languid palm trees. There are certainly views of the sea, but at this time of year it's mostly grey and bleak.

In fact, this mysterious private island looks for all the world like a giant rusting tin can bobbing about in the sea. But inside, accessible only by helicopter, there is a Jacuzzi, bar and swimming pool, as well as state rooms, bedrooms and entertaining rooms.

This is no ordinary island. It is a floating fortress, built in the 1860s to defend Portsmouth from the French during the Napoleonic wars. And it's for sale. There is no asking price, for who can put a value on this? But, as a guide, you will need to charter a helicopter if you want to go and see it, which might put off all but the most seriously interested parties.

No Man's Land Fort is the largest of four such forts and stretches to almost an acre in space. By the time these military outposts were completed, the French were no longer such a threat and they were abandoned. Used briefly during the two Great Wars, they were finally deactivated in 1956 and put up for sale in the Sixties.

This one is 200ft in diameter and provides some 55,000sq ft of internal accommodation. There's a basement and two further floors arranged in concentric circles, one of which is set around a massive glass-topped atrium. On the deck is a three-bedroom lighthouse with a 360-degree observatory, and, of course, a helipad: in fact, there are two. There is a boat launch and a winch, but it has fallen into disrepair and is presently unusable. When it works, you can be winched up the side of the fort, where there is a door which slides back and lets you in.

The agent, Knight Frank, is remaining tight-lipped about the vendor. A spokeswoman confesses she doesn't know anything about him, or her, or even them. It is, apparently, on a strictly need-to-know basis. Which somehow fits right in with the Fort.

For there is an unmistakeable atmosphere about this place. Stare at it, and you almost expect the roof to open and a helicopter to rise from the depths with an impassive scar-faced Blofeld clutching a sinister white cat and one of Her Majesty's top agents hanging grimly on to the back.

But assuming the buyer isn't a billionaire Bond villain in need of a secret complex, who would buy such a place?

It was converted into a luxury hotel in the early Nineties, but as it has lain empty for two years, one can only assume there wasn't much call for this type of retreat in the Solent. There is planning permission to build a floating harbour with 40 berths, so perhaps there are commercial possibilities. But before you think of ripping it all apart and creating some vast open spaces, you should know that it's Grade II-listed and is scheduled for English Heritage Ancient Monument status, which might limit any plans for dramatic loft-style conversions.

If you can afford the transport costs, and you fancy lounging about on your own private deck with a cocktail, or perhaps zipping along in your speedboat to visit the neighbours on their much smaller forts in the distance (which are already privately owned), then this might be the place for you. It would be a wonderful place for someone rich looking for an accessible retreat.

Word of warning: to anyone with plans to emulate the owners of Sealand, that other island fortress in the North Sea which declared independence from the UK in 1967, you should know that this is only two miles off the coast of the Isle of Wight. This means you are not in international waters and remain firmly under UK jurisdiction, which definitely rules out the Bond villain market.

Knight Frank: 020-7629 8171; www.knightfrank.com