The most common motivation for pensioners heading back into the jobs market was a desire to keep mentally active (61 per cent), although the need to boost retirement income (56 per cent) has also been driving retirees back to work.

Voluntary work was the choice of around 16 per cent of retirees who were back at work or plan to return in the future.

Even those who are earning are likely to take a pay cut – 51 per cent said their post retirement wages will be lower than their previous income in employment.

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It found that the most likely sectors for those working past State Pension age to find employment in are teaching and education, secretarial jobs and agricultural jobs.

According to the research, women who passed the State Pension age were more likely to have ruled out a return to work, with 51 per cent saying they were definitely retired compared with 44 per cent of men.

Stan Russell, retirement income expert at Prudential, said: “Although it’s striking to see how many retirees are choosing to return to work, it’s not optional for some people. While many say that working in older age is a good way of staying active, there are others who are forced to go back to work to make ends meet.

“Of course, there are real financial benefits from going back to work, such as earning extra cash and deferring taking the State Pension or income from private savings. However, for people who are hoping to give up work completely when they retire, saving as much as possible as early as possible in their working life remains the best way to secure the most comfortable retirement.

“The changes to pension rules that came into effect back in April have further increased the choices that the over-55s have to consider when preparing for retirement. Now more than ever, it is hard to overestimate the benefit of professional financial advice for most people planning for their retirement.”