IANAL and that goes double for Great Britain. That said, the general rule is that unless you go to some trouble to keep debts and assets separate they’re assumed to be common. In other words, her debts prior to demise are his afterwards, especially if they were acquired while they were married.
Assets and debts from before the marriage can usually be kept separate with a modest bit of care. E.g, my daughter’s student loans from grad school would not be her husband’s responsibility should she die now. Yeah, lousy example. But the one that came to mind.
