According to the survey from Baring Asset Management, 10 per cent of the working population – equivalent to some 3.5m people – don’t plan to stop working at all.
And a staggering 42 per cent say they are unable to predict when they will retire.
The figures represent a huge increase from when the research was last conducted in 2008, before the financial crisis took hold.
Back then, just one in 100 people said they didn’t know when they would stop working, while virtually no-one thought they would have to hold a job indefinitely.
The study, which was conducted among non-retired British adults, also revealed that almost 100,000 people who have yet to retire don’t plan to stop working until they are at least 76 years old. And 2.3m Brits don’t plan to retire until they are over 65 years old, an increase from 1.9m in 2008.
Marino Valensise, chief investment officer at Barings, said: “A combination of increased longevity, a rise in the cost of living, and people not saving enough means that more people are being forced to work beyond the age of 65.”
She added: “They simply can’t afford to stop working.”