Paddy Roy Bates, who occupied an abandoned fort in the North Sea and declared it the sovereign Principality of Sealand with himself as its prince, has died aged 91, his son said on Wednesday.

Michael Bates said his father died on Tuesday at a care home in Leigh-on-Sea, Essex. He had been suffering from Alzheimer's.

In the 1960s, inspired by the "pirate radio" movement, Bates set up Radio Essex on an offshore fort. When that was closed down, he moved in 1966 to Fort Roughs, a disused second world war platform in international waters about seven miles off the coast.