Thanks everyone who has posted. I received an email earlier from DH who says that there is ANOTHER instant access savings account which has £1000 in it. He has transferred £500 into our current account to make sure we're covered for everything until payday. So the immediate crisis is averted.
Rollercoaster, he says he is enjoying counselling because he seldom gets the opportunity to talk about himself.
If I was unflinchingly honest, Olivia, I'd have to admit that I've often spent a good deal more that £5 a week on myself. 
Thanks for the book recommendation, Kr1stina. I shall check it out.
I'm not defending him, Mrskeats, I've been feeling pretty angry with him for a very long time. Just trying to keep his shortcomings in perspective, as it's in no one's interests to go to war - least of all DD's.
43percentburnt, hugely helpful post, thanks. Much of what you've said I was either ignorant of or hazy about.
Do you claim cb and he pays the higher rate tax charge? Yes, I claim CB, which is paid into our joint bank account. He doesn't pay the higher rate tax charge, because he refuses to do a tax return and, so far, they have not rumbled him. This makes me worry that at some point we'll be clobbered by a huge tax bill, plus fines. I have nagged him about this, and continue to remind him every 6 months of so, but he does nothing.
Does he shop around for interest rates on his savings? I don't believe so. Sometimes tries to give the impression that he is financially savvy, by alluding to unspecified 'investments' that he holds and using highfallutin terms like 'fiscal responsibility' to describe his approach to money but, TBH, he seems pretty clueless much of the time.
Did he save the savings himself from wages or was it inheritance? Wages. He has been a diligent saver in the past, that's for sure, which is why I'm not interested in grabbing the money he earned/saved before we met, as there would be something very unjust about that I think.
He will go for 50/50 to reduce maintenance I'm worried he'll go further, and demand to be the main carer. He is absolutely resolute that 1. He will not give up DD, and 2. He will not give me any of 'his' money.
He will call you money grabbing and greedy. Yep, already has in fact!
I reckon your mum and sister know he's a bad egg but won't be totally honest as they don't want to ruin their relationship with you (ie you might tell him and then he encourages you not to see them). I think they are sympathetic to the difficulties I've been having, but also know that he's been a good Dad to DD and appreciate that he's reliably brought in an income over the years. He has not encouraged me not to see them, but he's let it be known that he'd like to be included in all the conversations I have with them regarding our marriage, says we are one family and should be working through this together. After I raised the idea of separating, he organised a meeting with my Mum to discuss the situation, which was apparently excruciatingly embarrassing for her.