The couple died in 2021, and their house was valued at £750,000, meaning their children will have to hand over most of that to the bank.

Shared appreciation mortgages (Sams) were only available from Bank of Scotland and Barclays between 1996 and 1998 and were aimed at helping older people release some of the value locked up in their homes.

However, many people have been left with huge debts after house prices have risen sharply since the mortgages were taken out.

Sams are not regulated, so complaints by borrowers are often rejected by banks.

The ombudsman has no jurisdiction over the subsidiary because it is not carrying out any "regulated activities," and a court case is brewing that could help decide how things pan out for the estimated 2,000-plus people who still have a Bank of Scotland-administered Sam loan.

The bank has confirmed that Sams were a specialist type of mortgage available in 1997-98, and that all borrowers were advised by their own solicitor and an independent financial adviser.

However, the bank is unable to comment further on the litigation.