A quarter of a million more people aged in their late 50s and early 60s are now working unpaid overtime than were a decade ago, a report says.
The TUC said the rise was out of line with much of the working population where unpaid overtime had fallen.
It said this reflected people working past normal retirement amid concerns about income in later life.
The trade union organisation said it had found that 660,000 workers in this age group put in unpaid hours in 2011.
Read More: TUC says more older staff working unpaid