Well, she is abusive of you on too many levels to even begin mentioning them in detail, so let me just say that you are a victim of economic abuse.

What country are you a citizen of and what is your immigration status in the United Kingdom? Since you mentioned working, you must have legal status and a work authorization. I am afraid that you need an attorney in the UK, unless there are enough people from the UK here to give you initial pointers. Clearly you cannot lead this kind of existence for much longer so you must start getting information and advice on how to part ways with her while retaining at least partial custody. She is a highly unusual person so you should be prepared for any kind of a scenario. She also is probably extremely vengeful (!!!), which is why getting legal advice as soon as possible is the most prudent solution. I know you do not have access to cash, but there must be some - they call them "legal aid clinics" in the US - something like this. Your situation is precarious - be careful and keep as much written evidence of what has been happening as possible.

Can you prove that you have no access to one of the two accounts? If you can prove it, then you have one piece of written evidence of being a victim of economic abuse. Everything else seems to be happening in spoken form so I am hoping that there a trail of breadcrumbs to show that she cut you off from one of the two joint accounts. Or does she simply have a password that you do not know? Can you still go into a brick-and-mortar bank branch to use that account?