It averaged at 7.9 hours a week, with the amount missed out in annual pay at £6,709 per worker.
Instant Offices found that Londoners did the most unpaid overtime in the UK, with 15.9 per cent working extra unpaid hours in 2020.
It estimates that British workers Lost £21.9 billion from unpaid overtime in the year, with the West Midlands totalling £2.12bn.
The more than three million Britons who have been working from home have accumulated 1.2 billion extra hours – an average of 7.7 hours a week – equivalent to an average of £7,300 a year of unpaid overtime.
More Covid news:
ONS data shows that although output per worker initially dropped 17.9 per cent in the second quarter of 2020 when the pandemic began, this quickly bounced back by 16.6 per cent in the third quarter. This suggests that as people have adapted to working from home, their output and the hours they work have increased.
Lucinda Pullinger, Global Head of HR at The Instant Group, said: "As we look at returning to the office, all companies have an opportunity to define a workspace strategy that aligns business strategy with supporting the wellbeing and engagement of its employees. This is imperative for a successful business.”