Workers in Scotland are doing increasing amounts of unpaid overtime and would receive an extra £4517 a year if they were paid for the additional hours they are putting in, according the STUC.

The number of employees in Scotland working unpaid increased by 20,000 in 2007, bringing the total to 436,000. The average amount of unpaid overtime is six hours and 54 minutes a week.

The STUC 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 February 22.

The trade union body has declared February 22 "Work Your Proper Hours Day" and is calling on employers to thank staff for putting in the extra hours and ensure in future they work their contracted hours.

The number of employees working unpaid overtime across the UK increased by 103,000 to nearly five million; about one in five of the working population. The average annual value of unpaid overtime in the UK is £4955 per employee.

Grahame Smith, general secretary of the STUC, said: "After years of progress, Scotland's long hours culture is enjoying an unwelcome renaissance and today's figures suggest many people are not even being paid for putting in these extra hours.

"Workers in Scotland are giving away over £4500 a year in unpaid overtime. That's too much time and money that could be better spent with friends and family.

"We're calling on all Scotland's employees, including bosses, to take a stand on Work Your Proper Hours Day' by making sure they take a proper lunch break and leave on time."

The pattern varies across the UK with Scots working longer hours than workers in Yorkshire, the East Midlands, the South West, and Northern Ireland. But they work shorter hours than in the north-east of England, the north-west, the West Midlands, eastern England, Wales and the south-east.

By far the most unpaid overtime is worked in London, where 741,000 people do seven hours 54 minutes a week, worth £7587 annually.

The STUC calculated the value of unpaid overtime using data from the National Statistics Labour Force Survey and Annual Survey of Hours and Earnings. Overtime is des-cribed as any work over the basic working hours included in a contract.

Regulations say that most workers cannot be made to work more than an average of 48 hours a week, but they can agree to work longer.