Ok, 1: you need to stop the joint therapy as it's not only unhelpful, but actually dangerous in an abusive relationship. Other posters could tell you more about why this is, if it's of interest to you. (Although I think you said it yourself "I went to pieces at marriage guidance when he was essentially doing a character assassination on me and I couldn't defend myself").
2: if you really want to put this issue to bed, you need to have that conversation. I suspect that part of you is reluctant to go back to work - and you have very good reasons for this (nobody in your impossible position would or could go back to work, just in case that wasn't clear). But you need to put that reluctance to one side and go in bouncing with enthusiasm like Tigger and say "I've decided to get a job in October! Let's figure out how we can make it happen! Can we have an hour to talk about it on [Sunday morning/Wednesday night/whenever you know he will be free]?" If he absents himself from the agreed time, you can keep pushing for that meeting, or at the very least refer to it next time he moans about you not working ([wide-eyed look] "but we haven't had my Back To Work house meeting yet, I can't go for interviews until we've done that, can I DH?")
Now: the meeting. Get it alllllll down on paper. Ask him how he's going to assist you getting back to work, or do he won't, what his alternative suggestion is. If you need training, the money has to come from somewhere, doesn't it DH? If the kids need looking after, someone will have to pay for it won't they DH? Keep putting it back on him to come up with solutions. And finally, when it becomes clear that you can't simply drop everything and magic up £700 a month, make your husband actually say the words "this isn't going to work". Or come up with an alternative.
Right now he has you, as I said, in an impossible position and he knows it. Stop hiding in the shadows and feeling guilty. Get it all out in the open. You have done nothing wrong. You need to stop feeling bad about the CC thing too. Absolutely stop allowing him to use this against you.
- If you reeealllly want this to stop - which I would - leave him