A file photo of Sealand.

For sale: the world's smallest country with its own flag, stamps, currency and passports.

Apply to Prince Michael of Sealand if you want to run your own nation, even if it is just a wartime fort perched on two concrete towers in the North Sea.

Built in World War Two as an anti-aircraft base to repel¹ German bombers², the derelict platform was taken over 40 years ago by retired³ army major Paddy Roy Bates who went to live there with his family.

He declared the platform, perched seven miles off the east coast of England and just outside Britain's territorial⁴ waters, to be the principality of Sealand.

The self-styled Prince Roy adopted a flag, chose a national anthem⁵ and minted silver and gold coins.

The family saw off attempts by Britain's Royal Navy to evict⁶ them and also an attempt in 1978 by a group of German and Dutch businessmen to seize Sealand by force.

Roy, 85, now lives in Spain and his son Michael told BBC Radio on Monday his family had been approached by estate agents with clients "who wanted a bit more than a bit of real estate, they wanted autonomy."

He suggested Sealand, which has eight rooms in each tower, could be a base for online gambling⁷ or offshore⁸ banking⁹.

Asked to describe the delights of living on what he described as a cross between a house and a ship, the 54-year-old said: "The neighbors are very quiet. There is a good sea view."