A private island in the Thames Estuary is up for sale at £50,000, complete with its own Victorian fort

There's something unmatchably romantic about the idea of having an island of your own. And while many that come up for sale these days are either dots on the map in the Caribbean or pristine white-sand havens in the Hebrides, there are exceptions.

One of those is Darnet Fort, an island on the River Medway — within the great arc of the Thames Estuary — that is going under the hammer via Savills, with a guide price of just £50,000.

It is, in other words, a place where you could conceivably build a home, and commute to the City via speedboat. Though a lot of work needs to be done first.

The Thames Estuary is dotted with small islands, going from the large — the Isle of Sheppey is over 23,000 acres — to tiny sandbanks which only appear at low tide. Though some are large enough to have been settled, most too remote or marshy to have practical use, and are uninhabited. Darnet Fort was an exception, thanks to its strategic location on the River Medway, downstream from the Royal Naval Dockyard at Chatham.

In the second half of the 19th century, with tension rising between Britain and France as Napoleon III took power across the Channel, Britain strengthened its sea defences across much of the country, and as part of that Darnet and nearby Hoo Island were turned into forts to offer protection to the vital base upstream at Chatham. Built between 1870 and 1872, Fort Darnet was originally designed for two tiers of guns mounted in a circle, with a boom strung between them — though rising construction costs meant that the boom was never implemented. Plus ça change.

To man the guns, the fort was built large enough to house a garrison of 100 men, and while it was used for gunnery practice it was decommissioned a few years later. It did briefly find use again, as an observation post in the Second World War.

The agents report that the fort 'is still in fair condition', though they note that, at present, the magazine level, originally used for storing ammunition, is flooded. It's also worth noting that Darnet Fort is scheduled under the Ancient Monuments and Archaeological Areas Act 1979; there is, as yet, no permission in place for development or alternative use — something which contributes to the very low guide price of £50,000. The existing owners have held the freehold for 40 years, using it for sunny afternoons of picnicking on their own island, but there's no doubt more could be done.

Could it be changed? Should it? Could you turn the place into an off-grid haven, from which you could get into central London, 25 miles or so away, on your own boat? Or perhaps helicopter? In theory all these things are possible, but there will be big hurdles to be cleared first. Good luck to all those who bid; we're fascinated to see what happens next.

Darnet Fort is being auctioned by Savills on December 10 — see more details.