Firstly, it would appear that you have submitted evidence of medical insurance. It is possible that they have not read it or overlooked it. Did they return this to you? If not, point out that you have already submitted it and state that they may overlooked it.
In the UK spouses have a legal duty to support each other financially, whatever their banking arrangements. If one spouse has sufficient savings or income, the other cannot claim any means tested benefits - income support, etc (unless they cease living together, bit that’s a different matter). Therefore, it would not be right for UKBA to insist on joint bank accounts. Your savings / income should allow your spouse to be considered self-sufficient for the purposes of EU law. It would certainly come into play if he tried to claim means-tested benefits, which is what was meant to be the purpose of the requirement in the first place. Point all this out and see what happens. Read the citizen’s advice guide. It’s under financial support (maintenance) half way down the page. In case you are in Scotland, the law is very similar.
http://www.adviceguide.org.uk/index/you ... rences.htm
Not that I am suggesting for second that this applies to you, but I can easily envisage a hypothetical scenario, where one spouse should not have full access to funds (mental illness, addiction, etc), but that would not relieve the other spouse of their legal duty to support the other financially. My point is that you should not have to have joint bank accounts to qualify.
If your husband was working or self-employed, it would simplify matters for you. Everyone’s circumstances are different of course.