If it were me, I would look at our household income, deduct all bills, food, travel to work, children's clothes and other household essentials and see what is left. Then agree to put some into savings for holidays, emergencies etc. After all the expenditure has been deducted the balance is split 50:50 or you both take an equal lesser amount to spend as you see fit.
You haven't said what your £750mth has to pay for, so it's hard to guess if this is reasonable. If all food and children's clothes etc have to come out of this then it may not go far, but if this amount is solely for you then to me this sounds quite a lot.
There may be some resentment in your case as some other posters have mentioned as to the time issue. If he is working long hours, he may question how you have time to fit in hair, nails, gym, lunches with small children. If he takes a lot of me time during the weekends, then it's fair that you have some during the week.
I think we should move away from calling this an allowance and see it more as a share of disposable income. Then the whole control issue won't exist.
A bit more detail from the OP is needed I think!