A learner driver and their passenger were released under investigation on suspicion of drug driving in Huntingdon.
Police stopped the pair in a silver Ford Fiesta while “on a driving lesson” in Ambury Hill on May 25.
The learner driver and his supervisor both failed a roadside drug test for cannabis.
Both men, aged 18 and 45 from Warboys, were arrested on suspicion of drug driving and have since been released under investigation.
In a statement on Policing Huntingdonshire, it read: “Police officers don't normally join you on your driving lesson unless something's gone spectacularly wrong.
“So far this month we've arrested 13 suspected drink/drug drivers across Cambridgeshire.
“Remember, you can report suspected drink or drug drivers 24/7 using our dedicated, confidential hotline on 0800 032 0845.”
Police have roadside screening tests for cannabis and cocaine. If anyone appears to be under the influence, they will be arrested and taken to a police station for further tests.
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