Adam... service intervals on trucks tends to vary according to usage, EG.a truck on motorway work using fully synthetic oil will run 50/60k or more(all trucks are in kilometers due to tachograph) whereas a tipper used on dusty/arduous site work would be a lot less. Trucks these days are much like cars , only heavier and more robust. They have less and less lubrication points, brakes are usually self adjusting etc, they are just so good these days.
To use a truck you need an operators licence, part of this, is a requirement for safety inspections. Companies have designated people to perform these duties,according to use this inspection may be weekly/monthly/or more. Everything is recorded(even a broken bulb) Traffic inspectors can enter your premises anytime they like and inspect any truck you have! They also have lap-tops,when they stop you on the side off the road with all your info on. If they pulled you on Monday in London with a (bad) fault, and again on say Friday in Scotland they would go straight to that fault and see if it was fixed.
Hope this explains a bit, it is one of the most heavily regulated industries in the country!