There was somebody hurtling around Bucks a few years back with a horse box with blue flashing lights. They were a self-styled horse ambulance. The emergency services politely pointed out to them that you can't put flashing blue lights on your vehicle willy-nilly.
However, on the laning trip we did last weekend I noticed Steve from Lanerovers had a yellow flashing light, plus a neon safety jacket in the back, which gave an amazing degree of credibility. Looks like a great way of avoiding unwanted complaints from members of the public.
David