Sadly the police can still issue you with a canary if they choose to, with 'H' plates.
Zeddophile, my local car club - Gippsland Car Club 'Sporting Register' has a delegated 'inspector' in the club (who is actually a specialist Porsche mechanic) that is able to sign off on the 'roadworthy condition' of a vehicle that is to go on 'H' plates. So no RWC required.
He is FAR more understanding on the rules & idiosyncrasies of classic vehicles, than any dumbarse RW mechanic I've ever met...
So yes, they do exist