Yes it is utterly illegal but no one has ever been prevented from doing so in my lifetime, the Police know the score and don't care. There are a lot of statutes that are seldom enforced, as it's not been in the public interest to prosecute. Not doing anything dumb as I suggested above keeps it that way.
If you ever attend an air display, they are common as muck.
Glasgow :
Tower 118.8MHz
Ground 121.7MHz
Radar 119.1MHz / 119.3MHz
spare ATC 121.3MHz
Signature 122.35MHz
Servisair 130.6MHz
Loganair Ops 130.65MHz
BMI 131.575MHz
Aviance 131.875MHz
Alba 122.05MHz
Menzies 131.4MHz
Think that's about it.