Image: Strutt & Parker

Welsh Napoleonic Fort For Sale on Private Island

Thorne Island – A Napoleonic Fort For Sale off the Coast of Pembrokeshire, Wales is Available Through Strutt & Parker with Offers Invited over £3m.

Once a key defensive stronghold during the Napoleonic era, Thorne Island stands proudly off the Pembrokeshire coast, its heart dominated by a striking Grade II\* listed fort. Built between 1852 and 1854 as part of the “Palmerston’s Haven defences,” it was one of twelve strategically positioned forts protecting Milford Haven—a major naval base at the time—against potential French invasion. Its imposing structure and commanding location at the entrance to one of the UK’s largest natural harbours made it a vital part of Britain’s coastal security. Today, the fort remains an iconic maritime landmark, its military past adding a layer of historical gravitas to its modern role as a private island retreat.

Covering around 2.49 acres, Thorne Island is now a secluded haven, offering unrivalled privacy and panoramic views of the bay and the surrounding Pembrokeshire coastline. Accessible only by boat to its private jetty, the island combines remoteness with an undeniable sense of prestige. It has a rich history of varied uses, having served as a hotel as well as a private residence. Registered as a Hotel & Premises (VOA Business Rates), it presents opportunities for both private enjoyment and commercial ventures, from a high-end hospitality business to an exclusive events venue.

The current owners have undertaken an extensive and sensitive restoration, breathing new life into the historic fort while preserving its original character. Works have included revealing original brickwork through sandblasting, upgrading renewable energy systems, stabilising the cliffs, and adding unique amenities such as a rooftop bar, an office in the former lookout, and a 10m hydraulic crane for boat and supply handling. Inside, the fort offers over 8,000 sq ft of living space with vaulted ceilings, exposed brickwork, sash windows, and wood-burning stoves. A large open-plan reception and dining area sits at the core, complemented by a modern kitchen, snug, and multiple flexible living spaces.

Accommodation includes five bedrooms, three of which are en-suite doubles with mezzanines, sitting areas, and direct courtyard access. Another bedroom offers sea views and a wood-burning stove, while a central fifth bedroom has the potential for subdivision. In total, the fort can accommodate up to 20 guests, making it ideal for gatherings or group stays. Additional facilities include five bathrooms, workshops, boiler rooms, and storage areas, along with the aforementioned glass-fronted cliff-edge office that offers a dramatic working environment.

Outdoor spaces are equally impressive, with a sheltered lawned courtyard, a rooftop bar and games room, and a large terrace offering 360-degree views. The island benefits from five private sea moorings, a rainwater harvesting system with potable water production, air source heating, underfloor heating, and solar power with extensive battery storage. Surrounded by caves, fishing spots, rocky outcrops, and sandy beaches, Thorne Island is an adventurer’s paradise—offering a rare chance to own a former Napoleonic fort that combines history, luxury, and complete off-grid independence in one of Britain’s most breathtaking coastal locations.

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