Over five million workers across the UK gave away £27.4 billion in unpaid overtime in 2009, according to research by the Trades Union Congress (TUC).
The study shows that 5.07 million people regularly worked unpaid overtime in 2009, a decline of 168,000 since 2008. Staff who did unpaid overtime worked an average of seven hours 12 minutes a week, worth £5,402 a year - the highest amount since records began in the late 1990s - and an increase of £263 since 2008.
TUC declared this day Work Your Proper Hours Day and will call on bosses to thank staff for the extra work they are putting in to help businesses through the recession.
Brendan Barber, TUC's general secretary, said: "The recession has forced many employees to do less hours in an effort to save jobs and this has also had an effect on the amount of unpaid overtime worked.
"Most employers are understandably focused on fighting their way through the recession. But they should not forget that working cultures such as pointless presenteeism - which keeps people at their desks for no good reason - is not just bad for staff but bad for business too."