best way to avoid gaining debt from a partner is to have a seperate bank account. if you keep things well and truly seperate it would be difficult to dispute later and formally - through insolvency or a divorce, for example. i would also recommend keeping scrupulous accounting records also, if that's what you are expecting!
The legal responsibility for the debt remains with the person who incurred it, and only that person can be pursued for it through the Court.
I think Ethel's 2nd paragraph probably refers to the possibility of the debtor becoming bankrupt. If that happened and it could be shown that the debtor had transferred assets or cash to other people in order to disadvantage his creditors then the Official Receiver could seek to undo the transaction.