On this day in 1967, a pirate radio operator took over a sea fort off the east coast of England and declared it a sovereign state: the Principality of Sealand.

HM Fort Roughs was one of several platforms – known as the Maunsell Sea Forts – built to protect Harwich and the Thames Estuary during World War II.

A rectangular, 51m x 27m pontoon base supported by two 60ft concrete towers, ‘Roughs Tower’, as it is also known, was constructed in 1942 and stands in Rough Sands, a sandbar seven miles off the coast of Suffolk and 10 miles from Harwich seafront.

Throughout WWII it was occupied by 150–300 Royal Navy personnel and used as an anti-aircraft base. After being used by the British government for various purposes, all full-time personnel were removed from the platform in 1956.

Rough Sands fort, since 1967 the independent Principality of Sealand.

In 1965, Roughs Tower was briefly occupied by Jack Moore and his daughter Jane, who squatted there on behalf of the pirate station Wonderful Radio London.

Then in the following year, Paddy Roy Bates, who operated Radio Essex, and Ronan O'Rahilly, who created Radio Caroline, seized it. After disagreements, Bates claimed it as his own – defending the fort against O’Rahilly with guns and petrol bombs.

[Read more: September 30, 1967 - 'Wonderful Radio 1', the BBC's first pop station, takes to the airwaves]

British Authorities ordered Bates to surrender – and in August 1967, the Marine Broadcasting Offences Act was passed, making it illegal for pirate radio stations to be operated by or employ British citizens. On September 2, Bates declared independence and deemed the platform the Principality of Sealand, titling himself Prince Roy.

Joan and Roy Bates, Princess and Prince of Sealand, in 1979.

In 1968, British workmen entered what Bates claimed to be his territorial waters and his son Michael tried to scare them off by firing warning shots. Firearms charges against Bates were dropped, however, as the court said that the platform was outside the three-nautical-mile limit of Britain’s waters and thus outside the jurisdiction of the domestic courts: a ruling that helped Bates’s claim that it was worthy of the status of an independent sovereign state.

In 1974, he and his wife (Princess Joan, pictured above) went on to create a constitution for Sealand and over the following years they also produced a national flag, national anthem, currency, postage stamps and passports.

Sealand currency, with the 10-dollar coin featuring the profile of Princess Joan.

An incident in 1978 also helped Bates’s claim. The platform was stormed by mercenaries led by a German called Alexander Achenbach, who declared himself the Prime Minister of Sealand. Michael Bates managed regain control and capture Achenbach – who was only released after a German diplomat from the embassy in London was sent to Sealand and negotiated for his release. Bates said that the diplomat's visit constituted de facto recognition of Sealand by Germany.

In 1987, the UK extended its territorial waters from 3 to 12 nautical miles – meaning that Sealand now sat in British waters. The platform continues to be managed by the Bates family as if it were a recognised sovereign entity, and is currently occupied by caretakers representing 'His Royal Highness Prince Michael' (Michael Bates), who lives in Essex. There are still debates over whether or not it is a nation.

Photo credits: Rex Features