Well he should have given you, at the very least, name, address, insurers.
Since he didn’t, you’ll have to contact him via plod. Go to them with the reg number and they should be able to track him down. They should (but probably won’t) be interested because he hasn’t given you his details which I think is a legal requirement. Once you know who he is, then get the costs of repairs to your bike and get back in touch with him. Make sure you aren’t hurt, bearing in mind that injuries may take some time to surface and could cost you through time off work and/or treatment costs.
You didn’t by any chance get a photo of the driver- that would be useful.
Be extremely cautious about accepting anything “in full and final settlement” or similar.
Any messing from him, fire up a lawyer