The rule also states you must keep your vehicle well-ventilated to avoid drowsiness.
For some, a heatwave may bring on a spate of the dreaded hay fever.
However, think before taking those medications. new-ish Highway Code rule forbids this.
Hay fever medication can result in drowsiness, making it dangerous to drive.
Being found to have broken this rule (rule 96 of the Highway Code) could land you with six months in prison, three to 11 points on your license, and an unlimited fine.