The figures, from Prudential, show that more than half of couples over the age of 40 are at risk of leaving one partner penniless because both of them rely on one single retirement income.
In fact, some 53% of couples in this age bracket have made no arrangements to ensure that when one partner dies, their pension will continue to pay an income to the surviving partner.
Women are the most at risk; one in five will depend entirely on their other half for a retirement income, compared with just 5% of men over 40.
However, a lack of preparation is common to both sexes, with one in seven Britons over the age of 40 unsure about where their income will come from when they stop working.
Prudential is therefore urging people to take the time to look into their retirement options, and consider taking out a 'joint life' annuity that continues to pay an income to a surviving spouse, partner or dependant after the annuitant dies.
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Vince Smith-Hughes, retirement expert at Prudential, said: "For couples looking to enjoy a comfortable retirement, organising and agreeing their income options should be a priority – long-term financial planning can be even more important than managing day-to-day-finances.
As pensions and annuities are complicated - and the decisions you make about them will have a big impact on your future financial stability - it is probably sensible to take independent advice when looking at your options.
However, there is also lots of free advice available on how to ensure you and your partner can have a comfortable retirement. The government-run Money Advice Service and The Pensions Advisory Service are good places to start. Read our articles: A simple guide to pensions and State pension: when can I retire?