In series 5 episode 2 the car ( SJH 499D ) was fitted with a Pye 6 Channel Vanguard AM25T
The Control Unit can be seen located in the glove box. The main tx/rx unit would normally have been located elsewhere.
The Vanguard models were superseded by the Pye Westminster and Olympic range.
The Pye ranges were widely used in various UK government departments and the military. They have also seen service with the emergency services in the UK, some ending their working lives fitted in taxis......
Production life: 1962 - 1970
Standard frequency range: VHF 25 - 174 MHz, UHF 450 - 470 MHz
Transmitter RF output: AM25T 20W, FM25B 60W, B100FM 100W
Primary model variants: B10AM, AM25B, AM25T, FM25B, B100FM, U30FM, VM, etc.
Below is a link to the service manual which contains some drawings.