Lloyds Bank is being sued in the High Court after selling mortgages tied to rising house values.
The case has been brought by 150 homeowners who were sold loans by Bank of Scotland.
The so-called shared appreciation mortgages, which permitted borrowers to take out a loan against their house provided that the bank received a percentage of the equity growth when the property was sold, were mostly agreed in the late 1990s. House prices have quadrupled since then, leaving homeowners owning hundreds of thousands of pounds more than their original loan.