THE UK's most northerly castle is up for sale - with a starting bid guide price of less than a one-bedroomed London flat.

The protected Grade A listed Muness Castle on the Isle of Unst, said to be the most northerly of the Shetland Isles, is to come under the hammer on Friday with a guide 'opening bid' price of £130,000.

The castle built in 1598 for Laurence Bruce of Cultmalindie, half-brother of the powerful Robert Stewart, 1st Earl of Orkney, comes with a baronial title and gold and copper mineral rights.

Designated as a national monument in 1953, it is being sold as an "opportunity to purchase your own 15th century castle set within 240 acres of land in stunning location".

READ MORE: The Cool List: Scottish castles you must visit

The sale by Future Property Auctions also includes 240 acres, a number of crofter's cottages, mainly in derelict condition, and barns.

HeraldScotland:

Source: Future Property Auctions

Currently Historic Environment Scotland (HES) run and maintain the castle as a museum but it is unclear if that will continue following the sale.

The castle which is normally free to visit and open all year round, is listed by the HES as closed, but that people can still visit the exterior of the site.

It is also unclear whether mining operations will be permitted on the land.

The auctioneers claim that gold and copper reserves were discovered in recently commissioned geological survey.

According to one analysis, the low price tag is less than the cost of a £140,000 studio apartment above a Chinese supermarket in King's Cross, North London - which has a double bed in the same room as the kitchenette.

Today the 73ft by 26ft castle retains circular towers at the north and south corners.

According to the auctioneeers, the ground floor and first storey "survive mostly intact with corbelling supports for small turrets on the east and west corners".

The castle is now roofless and missing its upper storey which is believed to have been removed to build the surrounding boundary wall.

According to HES, the castle is of national importance "because of what it contributes to our understanding of late 16th to early 17th century domestic and defensive architecture".

HeraldScotland:

In its guide on the castle it says: "Its significance is further enhanced by the role that its builder, Laurence Bruce, played in the political history of Shetland during the time of the Stewart earls of Orkney and by the potential that its below-ground remains have for shedding light on the material culture of the period. Its importance is reflected in its status as a Property in Care of the Secretary of State for Scotland."

HES further describes it as a "remarkably fine tower house of the late 1500s"

"Here it’s easy to appreciate how the family, servants and visitors would have used the internal space of the castle," HES says According to HES, the castle has other fine architectural touches, including a variety of gun and shot holes, small turrets with chequer-pattern corbels and dummy gunloops. It also has a scale-and-platt staircase and an integral kitchen.

A finely carved oak panel from the castle survives, suggesting its hall was once panelled in oak, according to HES. The panel is now held by the National Museum of Scotland in Edinburgh.

Stories abound about Laurence Bruce. He was accused and investigated by the Privy Council for oppressing Shetlanders, though several legends portray him in a heroic light.

His conflict with the earls of Orkney came to a head in 1608, when Earl Patrick chased Thomas Black of Whalsay to Muness with 36 men. He was unable to besiege the castle before he had to withdraw.

HeraldScotland:

The castle was attacked and burnt by privateers from Dunkirk in 1627, though it was reoccupied afterwards. It was finally sold by the Bruce family in 1718.

According to HES ithad fallen into ruin by the end of that century.

John Morris from Future Property Auctions said: "We always get wonderful unique lots that you would not get at any other estate agencies.

"Selling a part of Scottish heritage that comes with a Barony Title and gold mineral rights, it is truly a fantastic opportunity to purchase a unique lot not to mention the 240 acres."

The auction takes place on Friday on between 10am and 4pm.

HES has been approached for comment.