According to the report by the Institute of Fiscal Studies (IFS), and the National Association of Pension Funds (NAPF), women in their 50s are ‘under-shooting’ their life expectancy by 4 years, 84 instead of 88.

Men are undershooting by around two years (stating 83 instead of 85), when compared to national projections of life expectancy.

Joanne Segars, chief executive of the NAPF, said: “Fortunately, people are going to live longer than they think, but they are not planning for it, so they might find their savings and pension do not stretch far enough.

“Millions of people are within a decade of their state pension but have still not thought about how long their retirement might last.

“It’s worrying that so many over-50s are sleepwalking into their old age and are expecting to be better off than they will be. It does not help that the annuity market has become so tough.”

The report also highlighted that those approaching retirement (aged 50 to 64) with a ‘defined contribution’ (DC) pension are too optimistic about what their retirement income will be.

On average their DC pension pot would have to grow by 77%, or £20,200, to reach their expected income.

Segars added: “The average saver with a defined contribution pension is being over-optimistic.

“They need to see their pension pot grow by almost 80 per cent to meet their expectations. That is a huge ask if they are only a few years away from their retirement party.

“Over a third do not have even a rough idea of what their pensions might pay out. It is essential to give your workplace pension a regular health check, to see what it might deliver.

“It is not too late for the over-50s to take some control of their retirement plans by adjusting the amount they save, or how long they are prepared to work for.”

The report estimates that of those aged 50 to 64; one in four would need to save more than £60,000 before retirement to attain the income they expect.

Six out of ten have also never thought about how many years of retirement they might need to finance.

On top of that, a third of those nearing retirement in the next decade also have no idea of a rough estimate of what their private pension income will be when they retire.

Over-50s who are facing rising life expectancy will need to make adequate pensions provisions, particularly when their pension is the ‘defined contribution’ (DC) type that is replacing final salary pensions in the private sector.

The NAPF says that when combined with the current climate of very low annuity rates, many are likely to feel short-changed when they convert their pension into an annuity.

The study also highlighted the importance of shopping around for the best annuity rate when converting a DC pension into an income stream.

It found that, in recent years, only 28% of those annuitising bought one from a provider other than the firm they hold their pension with, suggesting people are not making the most of their savings pots.

Those who used the internet were twice as likely to buy an annuity from a company that did not provide their pension.