There are currently only two preliminary (road side) drug testing devices which have received type approval by the Secretary of State (Home Office), these are:
The Draeger DrugTest 5000, this device is designed to detect delta-9-tetrahydrocannabinol (THC, the main active ingredient of cannabis) and
The Securetec DrugWipe 3S S303G, this device is designed to detect delta-9-tetrahydrocannabinol (THC, the main active ingredient of cannabis) and cocaine
Found this online...seen them use roadside drug tests on police interceptors lol