Analysis of official government figures by the TUC reveals that those Britons who do are working an average of seven hours and six minutes a week in unpaid overtime – down by 18 minutes a week on the 2005 figure.

And if those hours were paid at the average hourly rate, then they would be taking home an extra £4,800 a year – or £23 billion in total.

Top of the league table for the amount of unpaid overtime worked is the north-east with seven hours 42 minutes a week. In Scotland the amount of unpaid overtime worked is only six hours and 30 minutes a week.

The TUC has calculated that if everyone in the UK who works unpaid overtime did all their unpaid work at the start of the year, the first day they would get paid would be Friday 23 February.

That is why the TUC has declared 23 February Work Your Proper Hours Day and is calling on employees to use it to remind bosses of their extra unpaid work by taking a proper lunch break and going home on time for this one day a year.

Employers should also use the day to say thank you to staff for their unpaid work, perhaps by buying them lunch or an after-work coffee or cocktail.

TUC General Secretary Brendan Barber said: “We work the longest hours in Europe, and too many workplaces are gripped by a long hours culture. There are some small signs that we are getting a bit better, but there is still a long way to go.

“That is why we say that employees should take a stand on Work Your Proper Hours Day and for just one day a year take a full lunch break and go home on time.

“We do not want to turn Britain into a nation of clock watchers, and few mind putting in extra effort from time to time when it is needed, but it is too easy for extra time to get taken for granted and then expected every week.”