We have a joint account for bills and separate accounts for everyday spending.
I have 3rd party mandate on his accounts and he wouldn't have a clue how to access his accounts without me handing him the instructions.
We have separate accounts because he works away and often spends a lot of money that he then claims back as expenses. Before we split them we used the same account and it go a bit complicated to gauge how much money was needed to make sure he never ran out, which could leave him stranded.
So now I put X from my salary into the bills account, on Standing Order so I can't forget. Then, from his salary, I make sure our accounts are both topped up to a set amount and on the 1st of every month I whack whatever is over and above into savings. We both have credit cards, so if there is anything odd we use them and I make a note to pay them off before saving anything.
And I save every spare pound... if it wasn't spent it goes into a savings account. I save equal amounts in his and hers savings. Equitable for us and the tax man.
It took me years to get to here, but splitting the accounts like this gave us both a really clear idea of what was being spent where. We have both earned more and less than the other. He has been made redundant a few times (weird industry) and we both shop for food, etc.
But we have friends who keep their finances totally separate. They pay into a bills account and whatever they have left is their own to spend. I don't know why or how that works, but each to their own.