Should anyone care to know I have done some research . . . .
A lockable, correctly fitted fuel filler cap is a requirement of the highways code and is necessary to pass a MOT test.If the police spot a vehicle without a fuel cap, or with a damaged fuel cap, this would constitute driving a vehicle in a dangerous condition, which would incur a three points penalty on their license and a fine of up to £5k for LGVs. If the perpetrator committed the offence within 3 years of a previous conviction for the same offence they would be banned from driving for six months.Any evidence that you have of drivers breaking these rules should be reported to the police.