Your definitive answer is here:
http://www.ofcom.org.uk/static/archi...fo/ra169r7.pdf
However, friends at Ofcom inform me that there is no actual 'enforcement' of this. They do not have the manpower to go around and stop you. Therefore the regulation will be applied on a complaints basis.
So provided that 'no one knows what you listened to because you told no one what you overheard' then you are
probably in the clear..........
Rest assured that one day it will go digital, but that will take years to get international concensus on the technology to use.