Originally Posted by
KelvinD
HD: Unless things have changed (and I know they haven't yet), police transmissions in the UK were never encrypted. Northern Ireland was an exception for obvious reasons. Many police, ambulance and airport authorities used MPT1327 trunked systems. I know Heathrow used, and may still use, MPT1327.
Haven't a clue what MPT 1327 is/was but I can recall police in Bucks using a 'duplex' VHF system whereby the 'station' transmitted on one frequency and vehlcles replied on another with 'beeps' being transmitted on the station frequency to tell everyone else to belt up.