Non-payer

His postal address?

If you have his postal address, and his name, then send him a letter before action, requiring the payment in full, or you will initiate a claim against him in the local county court.

[Edit]
Just noticed that it's only for £17. Even then, write the letter. And phone the police, report the incident as fraud, and obtain a crime reference number.
[/Edit]

That sounds like a lot of effort.