This actually makes me laugh, when the Police first stopped doing this & private companies took over the role I had a customer who put a few vans on the road for this sort of work, when he first came to see me about it he had all the documentation about vehicle specification & markings with him.
I drew up what was required for him to see & as soon as he saw it he asked me to make changes, despite me telling him that it wouldn’t meet the requirements the vans were done as he requested anyway. He worked very closely with lots of different police forces & not once did anyone mention the livery being incorrect.
Since then I have seen quite a lot of other companies doing the same thing & I have yet to see one that has been done in accordance with the regulations.
I’m not saying for one minute you shouldn’t do it correctly though Ewan lol,