If the mortgage was in the name of the deceased, with one or more other people, they are known as a joint borrower. There are two types of joint borrowers (joint tenants or tenants in common), and what happens to the property differs for each.
Joint tenants - their share of the property will automatically transfer to the other joint tenant and your loved one’s name will be taken off the mortgage (unless they were bankrupt, in which case their share doesn’t pass to the other borrower – it passes to the trustee in bankruptcy). You don’t need a Grant of Probate for this to happen – just the death certificate, which you should also register at the Land Registry to remove them from the property register.
Tenants in common - the share of the property belonging to the deceased won’t transfer automatically to the other joint borrower(s). Instead, it will pass according to the instructions they left in their Will. If there is no Will, the property will be passed on according to the rules of intestacy (rules that come into effect when someone dies without leaving a Will).
If you're the joint borrower and you're unsure what type of joint mortgage you had, we'll be able to let you know.