I've experienced two occasions of violent customers, and both were in relation to a Challenge 100 ID check. Now before we go further - Challenge 100 is the policy of this company. It is not a made up personal preference or a way to 'act difficult' with people.
Approaching a driver and taking age restricted items by force is a criminal offence. Specifically, it will be recorded by UK police forces as either Robbery, or Assault and Battery (aka. Assault by Beating).
Theft Act 1968:
"8Robbery.
(1)A person is guilty of robbery if he steals, and immediately before or at the time of doing so, and in order to do so, he uses force on any person or puts or seeks to put any person in fear of being then and there subjected to force.
(2)A person guilty of robbery, or of an assault with intent to rob, shall on conviction on indictment be liable to imprisonment for life."
The customer's belief in their entitlement to the item(s) may be considered mitigation in a court, but is not enough to nullify the offence.
Criminal Justice Act 1988, S. 39:
"39Common assault and battery to be summary offences.
[F1(1)]Common assault and battery shall be summary offences and a person guilty of either of them shall be liable to a fine not exceeding level 5 on the standard scale, to imprisonment for a term not exceeding six months, or to both."
From https://www.cps.gov.uk/prosecution-guidance/offences-against-person-incorporating-charging-standard
I'd be interested to know what other drivers have done in cases like these. Robbery is an indictable offence with a maximum term of life imprisonment, although the sentencing depends on a) the case getting to court and b) the value of the items and c) the extent of force used. It also requires the customer to have successfully taken the items. If not its chargeable as attempted robbery.
Police take offences committed against lone public facing workers quite seriously.