This via Digital Spy:
"Love them or hate them there are over 70 pirate radio stations broadcasting in London and the majority have been established for over ten years now. According to a survey conducted by Ofcom in 2007, over 800,000 people in London listen to the pirates.
If you listen to pirate radio in London then please spare a few moments to complete this independent survey about most established London pirate stations... http://www.surveymonkey.com/s/PirateRadioSurvey
So far over 300 people have taken part, results will be announced on January 14th."
There is also quite a discussion on this thread about London pirates and the interference they may or may not cause...