While it is expected that only a small fraction of the 15.7bn SSIA bonanza will be used to pay down consumer debts, the maturation of the savings accounts will free up badly-needed cash sucked into the enormously popular scheme over the past five years.

The 2.5bn that flows each year into SSIAs is exactly equal to the extra interest bills borrowers face as a result of rising interest rates, according to Dermot O'Leary, economist at Goodbody Stockbrokers.

About 180,000 people have already cashed in their SSIAs, with the rest set to mature by next April. Most savers were making the maximum SSIA contribution of 254 a month, which will be freed up as the accounts mature to help cover higher debt repayments.

"It turns out that the difference in interest costs for households in total equals the 2.5bn a year they have been putting into SSIAs, " O'Leary said.

"SSIAs are like an insurance policy against rising interest rates and the money can now be redirected from the savings scheme into paying off higher interest rates. You could say we've been very lucky, because SSIAs are rolling off just as the higher rates are beginning to bite."

Last Thursday, the European Central Bank raised interest rates for the fourth time in nine months, and two more rate hikes are expected before the end of the year.

Assuming that the banks pass on the latest increase in full to borrowers, an extra 125 per month will have been added to the cost of paying a 20-year mortgage of 250,000 since last November.

Coming on top of previous hikes, last week's increase could be the tipping point for many families with big mortgages, according to the Financial Regulator.

"The latest increase will impact most on people with larger mortgages and multiple borrowings, such as first-time buyers, people with investment properties or those with several variable-rate personal loans, " said Sharon Donnery, the regulator's head of consumer information.

"Some people may need to adjust their budgets to deal with this latest increase, so take time out to review your spending to ensure you can comfortably afford your monthly repayments."

There is no information available on the take-up of SSIAs among big borrowers. "It's not necessarily the case that the people who have SSIAs are also those who have the debt, " said O'Leary.

However, because more than two of every three workers signed up for SSIAs in 2001 and 2002, he believes there is a big overlap between savers and borrowers.