OP
Octopus
I'd look at any court option as an absolute last resort even if you have legal cover. Try hard to come to arrangement direct with him and if that fails go the arbitration route via your scheme if possible. Ending up in court without exhausting all other options is a lot of stress and expense and courts don't like cases where insufficient effort has been made to resolve the dispute before the case unless the amount falls under a small claims court which is geared up to sort out petty disputes quickly and efficiently.
If and I say if, this goes to Court then the first question the customer will have to answer is why they didn't invite you back tho complete the works.
Sit tight and see what happens.
What do your scheme recommend?