He has minus £33 a month according to that.

I was about to point that out.
he onyl earns £400, she could earn £4000 but cause of being declared bankrupt can't get a property.
I earn £400 per month, I look after the kids, my partner, the main wage earner is bankrupt and will have no chance getting a property with her name on.
I would not get a property that costs £500 per month on my own as i only work part time and do not earn enough money.![]()
Issue is he isn't earning enough to cover the rent entirely himself on a lot of places for rent and his partner while earning enough has a bad credit record and will be much harder to get accepted as a tennant by most landlord/agencies... usually in the situation where one of the tennats has a bad credit record, etc. the other(s) will have to sign a contract making them liable if the person defaults, but in this case they are unlikely to make that exception.
Although tbh from my experience a good number will eventually cave in if you push a bit... depending on the current demand.
So put the tenancy agreement in his name not hers?
Plenty of landlords out their that will bite your hand off for the rent, plus sounds like the guy you are renting off has been cutting corners.
Isn't there a way, perhaps costly tax-wise, to get your partner to create a company