Small Claims Courts. Check
this as well. You should also contact your local Trading Standards but in my experience they are about as useful as the proverbial chocolate teapot!
I had a seriously bad builder from Lancing in Sussex (Latham and Sons) whose work on a £29,000 job was so bad it cost around £10,000 to put right. He has repaid all but £400 so far.
First action is to investigate any 'associations'/'federations' to which the cowboy belongs. Beware - Federation of Master Builders was a BIT of help but quote "is mainly there for the builder" unquote.
You will need to take on a surveyor (ok, more expense but necessary), then write (recorded delivery) to the cowboy, itemising your complaint and telling him you are proceeding with small claims action. You can get a help pack on how to progress a complaint (and write the letters).
Persevere. Tell EVERYONE in your area how bad the builder/developer is, and make sure he knows you are. Consider local papers/TV etc. Get nasty.
Good luck!