Maven i think you've done too much thinking.The van is part of the job,when you are an outside engineer/tech thats where you carry out most of your work.So,you use the van thats provided by your employer.In the U.K private use is now charged by the mile to the employees,hence why most companies use tracker systems to monitor private mileage.The tax man no longer regards travelling to your first job and travelling home as private use (benefit in kind).All companies i know let lads take the vans home because
A:Its easier to travel to your first job,instead of going to the depot first.
B:To cover some out of hours calls.Its been known for lads to collect parts of other vans instead of waking up the gaffer to let them into the stores.

Some firms are now telling the employees that travel time to first and from last jobs will be docked,why because it saves them more money from nothing.Who suffers ? the same employees who you expect to make you money out in the field.