All those skipped lunch breaks and late evenings in the office accumulate over time - adding up to 39 days worth of unpaid work a year, on average.Britons clock up almost eight working weeks worth of overtime each year without being paid, according to TotallyMoney.com"There's a line that it seems many of us cross - we're giving our employers more time than we are actually getting paid for."The finance comparison website figured out that the average British employee works for free for 6.6 hours every week, rising to 7.4 hours in London, or 43 days of unpaid labour a year.London is surpassed only by East Anglia, home of Cambridge and Norwich, where residents clock up 8.2 hours of unpaid overtime a week, or 48 days a year.The survey of 2000 British employees found that people who work in information research and analysis toil away the longest without extra remuneration, racking up 11 unpaid hours a week, followed by performers and teachers, with about 10 extra hours each.Other professions clocking up more than seven hours of unpaid overtime a week include lawyers, events managers, insurers, sales personnel, engineers, farmers, management consultants and journalists.Employees putting in the least unpaid overtime tend to work in shift-based industries such as administration, security and leisure.While the average male employee clocks up an extra 6.4 hours of unpaid work a week, this stretches to 8.2 hours a week for women, working out to an additional 10 days per year of free labour.A recent report from the TUC found that five million people in the UK work more than their contract specifies without getting extra pay - effectively working for free during the first eight weeks of the year - which amounts to £31.5-billion of free work for their employers.The research found that CEOs, teachers and finance managers work the most unpaid overtime.Joe Gardiner from TotallyMoney.com says: "We all want to do a good job when we're at work, but there's a line that it seems many of us cross where we're giving our employers more time than we're actually getting paid for."The website built an overtime calculator to figure out how much more money you could be making if you were paid pro rata for all those extra half-hours throughout the year. ..