To play the devil's advocate

Obviously, lying to you is not on, but he's (also obviously) having cash flow problems - is he getting paid from the main contractor? - he's not done a runner, so I'd bet that he simply hasn't got the money and struggling to keep afloat.
If that is the case, protests outside the job site won't help.
DO NOT THREATEN VIOLENCE. EVEN IN JEST.
If he ends up beaten up by someone else he owes moneyto - you could be in the frame just from the posts on here!
I agree with the ideas expressed above - 7 days LBA (letter before action), then issue small claims.
Chances are that he'll declare bankrupt or make an offer to pay at a quid a week (if he does pay).
You'll be lucky to see any of the money - but if you can seize anything saleable (difficult if it's not your site, unfortunately), you might recover some of it.
But long and short of it is, threats - whether legal or violent - are very unlikely to do any good

I hope I'm wrong, but dealt with quite a few issues like this in last couple of years
