If he has a permanent job I would stick with it. OH has been on Agency work for a while now and on several occasions (including the recent Honda lay offs) he has been given very short notice, one employer two weeks before Christmas laid off all their agency workers
I hate my job too and would dearly love to be doing something else. I expect many others feel the same, though of course it also seems a bit crass to be complaining about being in work when so many aren't. Trouble is (stating the bleeding obvious) most of us who hate our jobs can't afford to take a pay cut as we are working for necessities rather than fripperies, and that's supposing we could actually find any new job at all.
It's an awful position to be in though - to feel, for example, stressed out, unable to sleep for worrying, working extra hours to accomplish what needs to be done but not getting paid for it (e.g. if you're technically self employed and working on a set contract), dreading each working day and so on. Sometimes, there really is nothing to be done to make a job more bearable and you have no choice but to trudge on. I've often heard people say your health is more important than your job - say, when contemplating a lower paid and less dreadful role - but if you're counting every last £ what choice do you really have ?
I feel very sorry for anyone in that position but I wouldn't take the risk of agency work vs a permanent position.
It is awful to be in a job you hate but the job market is just too fragile at the moment to take many risks. Is there any chance he can retrain in the evenings or weekends to be able to look for other kinds of job? I feel sorry for him but it is a big risk to walk away from a permanent job in your position.