As he says you can transfer any plate onto retention or to another car for the standard fee (£80 or so).

However I think J1-99 would have originally been sold at a higher price, so the owner might want a few £££ before they sell it.

The other problem is finding the owner, you can get owner's information under the Data Protection Act but you need a good reason - and apparently wanting to ask the owner if they want to sell their registration is NOT accepted. You could lie about the reason but if they found out you would probably get into some trouble.

You can get the make/model by doing a car data check at www.theaa.com

Gareth