A historic gun tower standing on the mouth of the River Medway has sold at auction for £159,000 - £9,000 more than expected.

Estate agents had banked on the enviable address of No 1 The Thames, as well as a massive drop in price, to finally get the military fort a new owner.

Three years ago, the Grade II listed installation off the Isle of Grain, which can only be accessed at low tide twice a day, was on the market for a cool £1.5 million.

Despite being marketed as a possible nightclub, hotel, outdoor pursuit centre, casino, or seven-bedroom mansion, nothing has been done to it and it has continued to fall into disrepair.

In the past, phrases such as "genuine investment opportunity", "unique location" and "character property" have rolled off the tongues of a string of estate agents.

But realistically, it’s thought at least £1m would be needed to restore it to its former glory - and nobody, so far, has been prepared to take on such an ambitious project.

It has no electricity or running water and is about four-and-a-half miles from the nearest railway station of Swale.

At high tide, the tower is completely cut off from the mainland and is accessible only by boat or helicopter.

The Martello-style property was modified during the Second World War but has barely been touched since.

Also known as Grain Battery Tower, its original purpose was to protect Chatham and Sheerness dockyards against French invasion.

Anglo-French tensions ran high in the 1850s and the nation feared a naval attack, so it was fitted with an enormous gun on the roof.

But artillery technology rapidly advanced and the construction became obsolete, almost immediately after it was built in 1855. It was decommissioned in 1956.

Jeremy Lamb, auctions director for Savills, said: “There is always excitement when unusual lots come along as they have a special power to capture the imagination.

“We’ve had water towers and military sea forts in our sales in the past but this gun tower is a first.

“A blank canvas with heaps of history and phenomenal sea views, not to mention its coveted No 1 The Thames address.

“Historically, rare lots like this have seen significant interest in our auctions.”

In 2004, it was bought by Simon Cooper, a builder from east London who acquired it from the Crown Estate for an undisclosed sum.

It was then snapped up by an anonymous property developer for £500,000.

Over the last decade, it has been on and off the market with nobody willing to take on the project long-term.