Hi - I'm pretty sure that there must be some that can be doctor referred and funded on the NHS, although I'd have thought they're going to be much in demand. Some of the people who I've met who say they went to rehab wouldn't have had money to pay for it, I'm fairly certain.
I suppose that AA / SMART are the obvious initial free services that are everywhere (and are free) - then he'll need to see what his GP says might be available to him and start pushing for it. I suspect it will very much depend on where he's based as to how much free help is available.