//Thanks B, so does that mean Mr Sunak, now has a criminal conviction ?//
No, because he has not been convicted in court (this is based on the assumption that the PM pays his fixed penalty and the matter does not proceed to a prosecution).
//Sadly UK law makes no provision in differentiating between the two.//
It isn’t sad. It’s simply a matter of fact. By definition, any transgression undertaken contrary to a statute or Common Law is a criminal offence. There is a distinction of sorts. Most motoring offences are “non-recordable.” This means, although the miscreant has a criminal record, it will not on any DBS checks.
//big constitutional thing about levying a fine without court action. Big no-no for us constitutionalists.//
Quite so, Peter. Only a court can levy a fine (although the financial supervisory bodies, I believe, are allowed to tern their sanctions as “fines”). All the rest are “penalties” of some kind. The crucial difference is that fines can ultimately be enforced by a period of imprisonment in the event of default but penalties cannot.