Nearly 30,000 people with a mortgage from Skipton Building Society could see their repayments rise by 40% from 1 March.
Skipton say extreme market conditions have forced it to withdraw a commitment that its standard variable rate would never be more than 3% above the Bank of England base rate.
From 1 March it will rise to 4.95% which could mean a monthly increase of £121 for someone with a £100,000 loan.
We hear from Skipton's Chief Executive David Cutter.
This item was first broadcast on Radio 4's Money Box on Saturday, 23 January 2009