About half a million people who are approaching the current state pension age (SPA) are too ill to work, the Trades Union Congress (TUC) has said.
The employment rates for people approaching SPA are 54% of men aged 60-64 and 62% of women aged 56-60, according to TUC figures.
The government announced in its October 2010 Spending Review that the SPA will rise to 66 by 2020.
According to the TUC's analysis, two in five people approaching SPA are economically inactive, with long-term sickness or disability cited as the main reason for not working.
The union argued that increasing SPA will not automatically extend working lives, but will instead leave this group of people too sick to work but to young to claim state pensions.
People who had previously worked in skilled trades, heavy industry and low-skilled jobs were most likely to be inactive due to poor health.
The figures said 24,899 people who are too ill to work were previously process, plant and machine operatives and 35,934 worked in skilled trades, compared to just 14,972 managers and senior officials, or 20,180 former admin and secretarial workers.
About a hundred thousand more people are inactive due to ill health than due to having taken early retirement by choice, the TUC said.
General secretary Brendan Barber said: "Accelerating the rise in the state pension age will simply push more people into poverty.
"We will end up with a new limbo zone for people in their mid-60s who are too young for a pension, but too old to have any realistic chance of a job.
"With a benefits system that gets meaner and tougher each year, even 66 year olds who have worked for decades before stopping work will be treated as work-shy scroungers.
"By raising the state pension age and ignoring persistent health inequalities, the government risks overseeing a dramatic rise in pensioner poverty."
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