Private Welsh island and fort on sale for less than one-bedroom flat in London

The Grade-II listed fortification sits at the mouth of Milford Haven estuary

Stack Rock Fort and its private island (Purplebricks.co.uk)

An entire island off the coast of Pembrokeshire is on sale for £400,000 – less than the cost of a one-bedroom flat in London.

Stack Rock Fort is a Grade-II listed fortification built between 1850 and 1852 to protect Britain from French invasion under the rule of Napoleon III.

The large, circular building offers a 360-degree view of the surrounding waterways and is connected to the mainland by a short boat ride. Interested parties (and seasickness sufferers) should note that there won’t be any viewings taking place in bad weather, Ross McKenzie of Purplebricks, the property agent looking after the fort, has confirmed.

Although the island is currently uninhabitable, the property "represents an enormously lucrative and exciting opportunity, with limitless development potential", says McKenzie.

"Imagine, for example, a cable car being built from the mainland which ferries guests over to a unique, boutique hotel? With the right imagination and investment, it could become a stunning property which would do wonders for the local area.”

Made up of three floors connected by spiral staircases, the building was once armed with sixteen 18-ton guns and manned by up to 150 men. It was manned by a small consignment of men during the First World War.

Prospective developers might look to the nearby West Blockhouse, one of the other three forts built around the same time as Stack Rock Fort to protect from invasion via the estuary at Milford Haven, for ideas.

Having fallen into disrepair, the West Blockhouse was bought by the Landmark Trust, a charity which restores important historic buildings as holiday lets, in 1969. It was restored in 1986 and today sleeps eight in quarters once occupied by 34 men and one officer.

Though located on the mainland, so more easily accessed than Stack Rock Fort, which occupies its own private island, the West Blockhouse is not without its peculiarities. Parking at the property is via a steep 45m footpath, for example, and there’s a drawbridge.

A quote from the West Blockhouse’s logbook highlights the extraordinary views afforded by the property, similar to those available at Stack Rock Fort:

“Where else would you get such a view? Ships going into the haven, gannets diving for fish, ravens overhead and wild flowers down the path.”

Nearby Pembrokeshire attractions include the Pembrokeshire Coast Path, empty sandy beaches at Sandy Haven and Lindsway Bay, and historic attractions like Pembroke Castle, which dates back to 1093.