that cant be legal!? lol i got stopped in my plain sliver omega because i had a security uniform on with a high vis jacket and the copper said he could do me for impersonating a police officer 
If he had said that to me, I would have laughed at him.
I would have laughed too.
I had a silver ex thames valley omega with the camera and screen on the dash, in full view, yellow jackets on etc... and they stopped us. nothing happened. as plain yellow jackets arent ilegal, and nor is having a monitor. depends who stops you, and of course, what your doing with the car. ifyour waiting in layby then chasing people, yes your gonna get your ass kicked!
But having a replica police car "historic police car" for shows is not ilegal.
cant have blue reflectors on if using it as daily transport, but if you have a full battenburg one and are on way to a show and have the sign on the car not in service, you are covered.