Some time ago they might have turned a blind eye to a truck parked on an industrial estate, but the councils now have parking attendants, not the traditional traffic warden. They are under pressure to reach targets and you were an easy target.
Of course for a 6:45 delivery in London you were probally on a hiding to nothing, either park outside and get a parking ticket or drive into the area and get fined for going down the road before 7am. 