Helpful suggestion follows for all such instances.
Recently I have had two similar experiences...one with H.M. Customs; the second with VOSA (the UK's commercial Vehicle and Operator Services Agency). Both situations concerned the legal operation of a large truck.
Having been challenged on a legal point about which I knew I was on solid ground I uttered the following:
"Certainly officer...but I will trouble you to state your request in writing."
On profering pen and paper both uniformed herberts took on a remarkably similar appearance. Both suddenly developed a fascination with their own shoelaces. This was quickly followed by furtive glances at their colleagues, rapidly accompanied by incohenrent muttering and, finally, by backward steps and various chuntering along the lines of 'Let that be a warning to you.'
On both occasions I am pleased to report I resisted the retort to "Go and takle a flying **** at a rolling doughnut," or something silmilar, but either way, have not been troubled since.
Police state?...Only if you let them