@Penistoe
I second withdrawing all the money from the joint account at a bank and leaving straight away. The sooner the better.
Me too! That money is yours, OP, you have every right to clear it out.
And talk to the council's housing department, explain that you're planning to flee an abusive relationship, you will have your son with you and you can't go to a refuge, and see what they say. (Councils vary in how they deal with this sort of scenario, but many will have temporary accommodation for people in your situation.)
The DA helpline is very good (0808 2000 247). As well as general advice, they can put you in touch with legal aid solicitors who can help. If you can bear to start compiling a log of incidents and ways in which your husband has been controlling or violent, this will come in useful later on.
You will almost certainly be entitled to UC once you are liable to pay rent. You can use one of the online calculators (Entitledto is the most user friendly imo) to see how much you would get, just put in a figure for the rent you would expect to pay.
Open your own bank account now, and you'll be able to get your wages paid into it. Time your exit for as close as possible to the first day that your wages will be paid into your own account.
I really hope this works out for you, OP. You will have the collective power of the MN hive mind supporting you! 