The UK brought a new law into effect in March 2015 which allows the UK police to perform roadside drug testing using a roadside oral saliva drug testing kits called Drugwipe. A positive result will result in the driver being taken to the police station for a blood test. The drugs that the Police may test for under this law include Cannabis, Cocaine, Ecstasy and Ketamine & Benzodiazepines although most police have just initially tested for Cannabis & Cocaine at the roadside.
Since the introduction of the new roadside drug test, some police forces across the UK, have been finding around a 40-50% positive rate on the drivers they have drug tested.
Oral fluid mouth swab saliva drug testing kits with UK Police 6 roadside combination