Royal London has calculated that the majority of interest-only borrowers looking to move to a Retirement Interest Only (RIO) mortgage to help them at the end of their mortgage term will not have saved enough into their pension and so would struggle to meet the ongoing repayments in retirement.

The insurer says that with official figures showing that around 12 million people are not saving enough even to cover basic living costs after they retire, very few will be able to afford the cost of servicing a mortgage debt in addition. As a result, many will find that they fail affordability tests applied by RIO mortgage lenders.

Royal London has estimated that someone on average earnings who wants to maintain their standard of living into retirement needs a pension pot of around £260,000. But this assumes that they will have paid off their mortgage. If they need to take out a mortgage for £121,000 to clear their interest-only debt, the mutual insurer calculates they will need an extra £118,256 in their pension pot to service this debt for as long as they live.

Whereas the affordability test for a standard working-age mortgage relies heavily on the income of the highest earner or joint earnings, in retirement the lender has to look at how the mortgage interest will be paid after one partner dies. This means that it is the income when one partner becomes a widow or widower that determines if the mortgage is affordable. With many pensions stopping when someone dies or passing on only a modest percentage to a surviving partner, a mortgage that can seem affordable when both partners are still alive can become unaffordable if one dies.

Royal London is encouraging couples to find out what will happen to their pension income when one partner dies so that they have a realistic idea of how affordable an in-retirement mortgage would be.

Becky O’Connor, personal finance spokesperson at Royal London, said: “The introduction of RIOs may give false hope to hundreds of thousands of borrowers with interest-only loans they can’t pay off at the end of the term.

These loans might seem like the perfect solution, but in practice, because of affordability criteria, they will not be the answer for most people.

“Generally speaking, pensions are not designed to cover housing costs. ‘Target pot’ estimates assume that people who are homeowners have already paid off their loans and will only need to cover other essential living costs, like food and energy bills, in retirement.

“So even those who have a ‘decent’ pot size of £260,000 might find they wouldn’t have enough income in retirement to pay RIO mortgage repayments and still maintain a decent standard of living.

“With many people not saving enough in a pension even to cover basic living costs in retirement, many borrowers are likely to have an application for a RIO mortgage rejected, or be offered a much lower amount than their shortfall.

“It’s likely that uptake of RIOs will therefore be reserved for those endowed with the most generous pensions, or income from other sources such as property or work.”