BBC Radio 4's Money Box was broadcast on Saturday, 31 January, 2004 at 1204 GMT.
The programme was repeated on Sunday, 1 February, 2004 at 2100 GMT.
The shortfall on endowment mortgages has more than doubled and could reach £30bn, according to the Financial Services Authority (FSA).
One month ago, the Association of British Insurers (ABI) told this programme that 1.5m people would have to find extra money to repay their loans, and that half had already done so.
But now it has emerged that 3.5m homeowners are facing a shortfall.
We were joined by Louise Hanson, Policy Officer at Consumers Association to discuss the findings.
Producer: Penny Haslam
Presenter: Paul Lewis
Reporter: Louise Greenwood
Web Producer: Nathalie Knowles