It tells the story of a pirate radio station in the North Sea, presumably based on the real-life Radio Caroline, which was closed down by the authorities in 1967.
Anyone under the age of 40 who watches this superficial film should not imagine that it is remotely historical. For example, whenever there are scenes of young people partying or listening to pop songs, there are invariably a number of black people intermingling on terms of perfect intimacy and equality with whites. The suggestion is that Britain in the 1960s was a well integrated society without any racial tensions. It wasn't.
An even more blatant rewriting of history in the film has a Conservative government closing down the pirate radio stations when it was, in fact, a Labour government under Harold Wilson that did it. The minister responsible in the film is a repressed and highly unpleasant Tory toff with more than a passing resemblance to Hitler, played by Kenneth Branagh. Mr Curtis's wholly inaccurate cultural message is that nasty Tories were trying to spoil the enjoyment of a joyful, colour-blind England.
I don't expect historical accuracy at the cineplex, but this is extreme even by Hollywood's standards. Making the Conservative Party the villain of this story is like making the Republican Party the racist enforcers in a tale set in 1950s Alabama. Not only was Wilson in power at the time, but Radio Caroline regularly attacked the Labour Party. The Tories not only failed to lead the charge against the pirates, but some of them bought ads on the offshore stations (as did some Scottish Nationalists). There certainly were Conservatives who opposed the broadcasters—one Tory MP accused them of "providing what people want," which sounds good to me but he intended it as an insult—but it was Labour that pushed through the Marine Broadcasting Offenses Act of 1967, which barred British citizens from aiding the pirates in various ways, most notably by advertising on their shows. (Contrary to the report quoted above, Radio Caroline didn't close down that year, but it was crippled considerably.)
If Curtis had set his movie during the second wave of British pirate radio, when hundreds of urban stations playing reggae and R&B cropped up in the '80s, he could have cast the Thatcherites as villains without abusing history. (Margaret Thatcher may have championed individual initiative in her speeches, but when people pooled their pennies to start stations without the state's permission, she cracked down.) But that would entail giving up his Swinging Sixties setting and soundtrack. So he rewrote the past instead.