@Namechangesensitivemoney
*On the face of it, you personally actually have quite a large amount of disposable income (£400+ per month) plus very few responsibilities. It may not be about the actual amount of money per se, but about the fact that he has to always be responsible for finding the money for everything. To him it might seem like his money is "family money" to be spent on everything needed for the family, and your money is mostly your own pocket money for you to spend without having to worry. It might make it easier to arrange money differently. All money into one joint account, and then say £200 a month each into your own "personal spends" accounts. Everything else sent by DD to bills account/savings account/tax account/groceries account etc so its easier to see that the majority of money is "family money" and you have equal "spends". You can then both take equal responsibility for budgeting and dealing with savings/large bills and repairs. No-one then gets stressed if the washing machine packs in etc as there is joint money saved to deal with it.
I wouldn't expect a family with one person on £40k and one on disability benefits to be able to afford for any one person to have £400 per month as personal spends, although I guess being mortgage free may make that more possible*
I'm not sure why you seem to think it is only me having some money extra each month when he earns much more? 
Sorry for the late reply, I've been off having dinner etc.
In our household, the biggest expenses by far (apart from school fees which I assume you don't have) since we are also mortgage free are the the things that I'd listed, that you hadn't mentioned who was covering. We don't have anything like £400 per person personal spends despite a considerably larger income, and I would suggest if he is regularly paying into pensions, maintaining the house and the car(s), paying for fuel and all the other stuff that I mentioned above, then he will have basically very little left from a £40k gross income. No way could all that be paid for in £500 a month - that's basic CT/utilities etc only really, and doesn't look at the bigger one off expenses or any kind of preparation for the future.
I think you assume he has a much bigger amount of "spends" than you, but if he's having to pay for all of the family expenses bar food/healthcare on a £40K income, he likely doesn't have anything like as much left as you think. I know you have now clarified that you pay school uniform/shoes etc too, but these aren't the big expenses.
Who pays to replace the washing machine/dryer/oven when it breaks down?
Who pays to fix the boiler when in breaks down?
Who buys the car(s) and pays for car insurance/car repairs?
Who pays into pensions for you both?
Who pays into regular savings for the family?
Who pays for new kitchens/bathrooms?
Who pays for holidays and days out?
Who pays for maintenance and redecoration of house and garden?
Does he carry the financial "mental load"? The things listed above probably need about £1000 a month at least to budget for, somewhat more if you want decent pensions, family holidays etc...
I really think pooling income and then equal personal spends is the way to go, as it shares the burden and responsibility equally. You may well end up with more personal spends, but I think you might be surprised at how many costs there are over and above simple utilities.
Of course he might just be being tight, and squirrelling away thousands in his own name and leaving the house to fall into disrepair and not savings for the future or saving into pensions - I don't know!