Under section 7 of the Theft Act 1968 there is no distinction between theft from a work vehicle and theft from a commercial building. The theft offence would apply regardless of where the theft takes place.
Theft from a commercial building could potentially also amount to burglary if a person enters the building as a trespasser. However, theft from a work vehicle could only amount to burglary if the vehicle was inhabited. The requirement for entrance into a building (including an inhabited vehicle) is a fundamental part of the law on burglary that the Government has no intention to change.