@Alwaysforgiving
He's just complained about a bookshelf that we bought more than 3 years ago (and it was cheap, because well we didn't have a lot to spare...) Those type of comments really irritate me, it's not like we bought cheap things for the sake of it.
I have read all the various threads.
You sound very insecure when it comes to your marital relationship. This is likely a pattern for you going back years with previous relationships so it would be good to reflect on this.
You over-compensate for your feelings of insecurity by trying to control your environment.
In this case your husband is terrible with money and clearly immature.
The situation is obvious: the more you push him about money, the more he will push back against you. The trend is easy enough to spot after going over your various threads.
Stop auditing his accounts and investigating his finances. That does not help the marriage. It just makes it worse because it causes a snowball effect.
I am not going to sugar-coat things;
Your marriage is in serious danger. Please do not excuse his behavior, or your own. At the end of the day, you are raising kids who will end up absorbing all of this conflict. This will cause lots of problems later on.
What you need to establish are respectful boundaries.
He puts in X, and he does not have to account for the extra £200 (or whatever figure you calculated before).
Having said that, what you can do is not give him access to your shared credit card (I am assuming it is on the joint account). I would cancel it. He can have one based on his own account, and you keep yours on your own account.
What this does is tell him that while you respect his financial privacy, you will not be subsidising him further via your own money. He needs to use his own.