Don't worry about him using your bank account, at the moment.
The problem will be that on a joint claim, you are both responsible for letting benefits know when there is a change of circumstances, and neither of you did. You both let this go on for so long that there is now a very large overpayment. You were both aware, so this is intentional fraud. Even if you didn't see the money going into your bank account, you knew that you were getting both wages and income support.
If your husband is abusive and controlling and you were scared to tell the benefits agency, they may make allowances for that, but you would need evidence of it, and you would then need to leave him. You would not be able to tell them that he is controlling and abusive and then stay - you would be failing to protect your child, and yourself.
Was it your claim, that he was added on to? Have you had your income support or housing benefit reviewed in the last 12 months, and if so, did you verbally agree (or sign to say) that your circumstances hadn't changed?
As you've been overpaid by such a large amount, do you have savings?
A custodial sentence is usually the last resort in benefit fraud cases - prison costs the taxpayer money. However, this is a serious case. It has gone on for an extended period, it was deliberate, it amounts to over £5k.
There are mitigating factors, which are that you have a baby daughter, but if SS deem his mother/foster care appropriate, your views on that won't matter, unfortunately. Like I said earlier, if you are alleging that you are abused, that is also a mitigating factor, but you'd need proof and you won't be able to stay with him afterwards.