BBC News
By Andy Verity
image captionVanessa Bampton is one of thousands of mortgage prisoners
MPs are challenging the government to live up to a promise to help homeowners trapped paying high interest rates because the Treasury sold their mortgages to unregulated firms.
Since they cannot switch to a better deal, an estimated 250,000 homeowners are forced to pay standard variable interest rates.
These are well above what a competitive mortgage would charge.
But moves to ease their plight are being blocked, MPs say.
The House of Lords has passed an amendment to the Financial Services Act to cap rates for borrowers in that position, known as "mortgage prisoners".