Some pretty god advise above but personally I'd get the work done and send him the bill. When it doesn't get paid go on-line and put in a claim in the small claims court (you can do this on-line) anything he/she says about what you've signed refer them to "unfair terms in consumer contracts regulations 1999", basically anything they say in the contract is invalid is void if they've not done the job professionally.
Just because you signed a contract doesn't mean you've signed away your rights an incompetent survey is a "fault good or service" no two ways about it.
Keep all the evidence, photos or whatever then hit him with a claim, put up or shut up, I doubt it'll ever get to court, he'll bottle it and pay up.
K