LoW we've discussed this before haven't we?
Your DH has lots of reasons for a good legal case against his employer, health and safety issues, non-payment of monies owed, denial of basic employment rights, all sorts of things.
Really your best bet is to go and see the CAB and talk through it all with someone - there's quite a lot to pick through in terms of different laws they are breaking/responsibilites they have.
So there should be minimum difficulty bringing a case against them, but the trouble is if he doesn't want to leave the employment and is scared of repercussions if he kicks up a fuss about any of this, that makes it very tricky as I am sure you appreciate.
If his boss has made threats or anything of that kind which makes you concerned about 'repercussions', is it something you would consider going to the police about?
It's difficult for me to advise given what you've said about not wanting to leave/make a fuss, but I would strongly recommend you both go down to the CAB and see if you can have a chat with someone about all of this and discuss your options.
Regardless of money/references I really think his best option is to leave. I don't know anything about benefits but it sounds as though he is not going to get much money out of this company anyway, at least in the short term, so wouldn't it be better to leave and go on jobseekers allowance or whatever benefits he could get while looking for something else? I'm not convinced he'd get a decent reference either so it might be best to write off both those things and just get out of such a horrendous situation.
Do consider having a chat with CAB about all this and about what action your DH could take. There is no doubt this company is behaving atrociously and illegally and your DH needs to work out whether he is prepared to take any action, or whether he wants to walk away.
Good luck to you both, sorry you're in such an awful situation.