Using 2 number plates-is this legal?

[pinkmagic1]

DH was involved in a motorbike accident approx 3 weeks ago. The bike is in mess but thankfully DH escaped with minor injuries.
A young lad pulled out of a side road without looking into DH's immediate path and DH went into the side of him. The police were involved and thankfully there were quite a few independent witnesses. However the number plate displayed on the car is not recognised on any database. The police have provided us with another number plate to which the car is registered and insured and have assured us all is fine and we should have no problems. The 3rs party has not reported the accident to his insurer and is basically ignoring all calls and correspondence.
Is it legal to have 2 number plates? The one on the car looked like a private plate but surely you have to register these before you can use them without displaying your other plate?

Sounds dodgy to me

Do the number plates correspond in any way? Its not the same plate stylised to read differently is it?

No, completely different plates. The funny thing is the police have assured us its fine, however I smell a rat and the insurance company and solicitor also think its dodgy.

how do the police know what the correct plate should be?

Ask the Police to look into the accident more closely and for them to consider prosecution.