What do you say to the rozzers when you get stopped for something petty?

a little background reading so you know what 'service' standards to expect

politely ask the officer to produce their warrant card, to reassure you that they're not some fule on a merry jape,they can get disciplined if not carrying.

Useful link, thanks for that. Most interesting is that you do not have to give your name, address or date of birth unless being charged with an offence. I bet they gloss over that as much as possible in practice.