Close to 400 suspected pirate radio stations in London have been shut down over the last two years, according to figures released by Ofcom.
In response to a Freedom of Information request, the communications regulator revealed nearly a quarter of the raids took place in Haringey, north London.
It says that despite the advent of internet radio and the introduction of community broadcasting licences, pirate stations remain a problem because they can interfere with vital comms channels used by the emergency services.
"It's not about raising revenue," Ofcom's head of spectrum enforcement Clive Corrie told the London Evening Standard. "It's about protecting the spectrum from harmful interference.
"Last year Ofcom received 53 complaints of interference to aviation services - ground-to-air radio location and radio navigation systems."
He added: "It's a big problem, especially in London. There are about 70 active stations in the London area. In the whole of the UK we've got something like just over 100.
"From the enquiries we've carried out, this problem doesn't exist in New York or Rome or Paris - it's a London phenomenon."