It depends what they mean by "formal warning". There really is no such thing in law for an adult. This is cycling job an offence or a non-compliance, not a recordable crime, so community resolutions etc won't apply.
I don't know what the local processes are but i suspect that for those who choose to co-operate they simply log details on their intelligence system, and issue a letter telling them the behaviour is unacceptable, so it's on the police local records but in no way forms part of any criminalr ecord or process. It might be formal in the sense that the Police have issued it, but it would hold zero legal weight. It's the sort of scheme whereby they hope the sensible and otherwise law abiding citizen may learn from the experience and not do it again. If my guess (and it is just that) is correct it wouldn't be disclosable on a CRB check, but anyone who's job relies on such things should really be a bit more conscientious about the laws they break if they're that worried.
As it happens he got incredibly lucky not to get a spell in the chokey for contempt, never mind the rest of it.