London Pirate Frequencies is a nice short film presented by Matt Mason, tracing the story of free radio from the 1950s/60s forts in the Thames Estuary through to London tower blocks today. Current stations featured include Kool FM, Rinse FM and Flex FM.
I like Mason's comment about the contradiction between pirate radio's audibility and its invisibility: 'the thing about pirate radio in London is it's kind of everywhere, it's hidden in plain sight. If you turn on the radio, you tune the dial left to right you'll find a station but if you look around you you're not going to see them and they're literally all over the place. They're in residential neighbourhoods, in big tower blocks... there are pirates transmitting, about 80 stations across the city still exist today'.
There's a bit of a debate about whether the internet is killing off free radio on FM. It's true that anybody can now stream music via the internet without taking risks climbing up tower blocks and breaking the law. Most of the established pirates now also broadcast online and reach people all over the world - perhaps in the future they'll just be token FM broadcasts to give a sense of realness/London grounding to the deterritorialized online operation.
What I would miss about the loss of FM is the sheer randomness of coming across an unexpected signal while scanning the frequencies. Also radio is in some ways harder to censor than the internet. Repressive governments, like in China, can block access to websites but anybody with a radio can pick up a signal without the police or anybody else knowing they're listening to it.