It's quite a bit when there is no mortgage, after around £500 for monthly bills that is over 1K left...
OK, so out of that £1,600 he pays £500 of day to day bills. And then (to make it equal) let's allocate £400 spends to him to match yours, that leaves £700.
That £700 has to cover all savings, all pension contributions, all holidays, all repairs, all home and garden maintenance, replacement and maintenance of car, boiler repairs/replacements, redecoration costs, replacement appliances, budget for Christmas etc. I can see how he'd struggle. And it would be really stressful having to be the only one responsible for the family with such a small amount to juggle.
As a guide, we have £800 per month "family spends" which covers incidentals needed, minor repairs and maintenance, kids days out, new appliances, kids pocket money, mobiles, passport renewals, haircuts, takeaways, meals and days out and just general things that we need cash for day to day. We also save £200 a month towards holidays, and £150 per month towards birthdays and Christmas. We also put away £300 a month to budget towards major household repairs (so new kitchen/bathroom etc), and £300 a month towards car costs and repairs and replacement cars. So even then, over and above the food shopping and the basic bills we're looking at £1750 per month before we're even considering pensions and long term savings or allocating personal spends.
Our income is more than yours, and I think we have more responsibilities, so it'll likely cost us more, but no way could we afford to have £400 a month each unencumbered "personal spends".
I think, because you are not responsible for them, you are blissfully unaware of many of the costs of maintaining a house, car and family, and you aren't recognising how many demands he has on his money.
Once again, I'd suggest that pooling all income, and then taking a set amount of spends each, and both taking responsibility for managing the savings/house repairs/maintenance/holidays etc is a much, much fairer way of doing it. I personally like lots of separate pots for different kinds of spends, as it really helps to budget for long term things such as updating kitchens/bathrooms/cars etc, which can be expenses which become invisible otherwise.