What is specifically illegal is rebroadcasting aircraft communications (and other communications, police, etc.). I have this on pretty good authority but I've yet to see the complete law with my own two eyes.
I know that we had Heathrow on here a while back and a bunch of people wrote to me screaming bloody murder and chastising us for having it. There are a lot of people who love to spoil the fun for others.
So that, and especially the important fact that it appears to be illegal, has forced me to refuse any feed offers from the U.K.