Legal Advice Needed Urgently - possibly being screwed over by HR!

Shame to hear this T.
I don't have any relevant advice on how to go back to HR. In the wider context of these changes at your workplace I'd say do apply for the position in the other division which you mentioned as being ideally suited to you. (and which will be externally advertised). Much better to try for this than never test the water and later regret it.
It could well be that your unique knowledge of CPD is the reason for keeping you in the 'admin' role. And as such they need you and trust you. Would it be tolrable to sit things out for a while? Perhaps some opportunity may yet arise out of the flux in the system?

This is probably what I'll do.
It just really grates that the bullies are gonna win (in the short term - mwah ha ha ha - I shall piss in their cereal).