Generally you have to let them finish the job, ordering off site may not have been the wisest decision
Skenk, I am horrified that you suggest that a crap builder should be allowed to finish a job. Why would anyone in their right mind throw good money after bad, and then have to pay even more to get the shoddy work rectified.
Sorry Commando, you've been well and truly stuffed, and even if you took them to the small claims court, as you've got nothing in writing, I expect you'd get nothing back, and even if the judgement went in your favour, he'd just move to Spain earlier.
Do not, under any circumstances, let them do any more work, and whoever you get in to rectify the work, ask to see more than one job that they've done. Talk to your local trading standards office about them, and also contact the gas safe register if the plumber did any gas related work; likewise contact the NICEIC in relationship to the electrician, and also your local building control to check which regulations that they have broken over the work they've done.
It might be a complete waste of time contacting you're local police station over your concerns about any potential retaliations from them, but it won't do any harm either.
Best of luck.