So wait, you've been owed wages for six months? And you're
still working for these chumps?
Well, you definitely need to take action, try and get as much paperwork/evidence as possible: time sheets, anything you've sent in writing to your employer, and so on.
Your best bet is likely going to be small claims court, but CAB are definitely best to advise you. I expect they'll tell you to total up all the money you're owed and put a demand in writing, so then it's up to your employer to either pony up the cash or to prove that the amount is wrong.
And definitely start looking for other jobs. Any employer who treats you like this definitely isn't worth working for.