The law that applies to joint debt is called ‘joint and several liability’. This means that both people named on the debt are jointly liable for the full amount; i.e. not half the balance each. If both people named on a debt are made bankrupt, the debt will be written-off.
In some cases, one of the people named jointly on the debt does not want to go bankrupt. It could be that this is the only debt they have, and they are otherwise in a strong financial position.
Following the bankruptcy order, the bankrupt person would not need to make further payments towards the joint debt. The person that is jointly liable for the debt (but not made bankrupt) must continue to honour the full financial commitment to the creditor. They will take on sole responsibility for the debt.