Corporate entertaining and people taking time off to go shopping Christmas will cost the British economy £8 billion during December, new research has estimated.
The study by catering company Avenance suggest that, from 18 December, with five full working days to go, nearly half the UK's workforce will have hit what it called "festive fizzleout".
This was where employees were spending more of their working hours worried about Christmas festivities than work, with a marked effect on productivity, said Avenance.
More than two thirds of workers polled by the company openly admitted they were less productive throughout the entire month of December compared with other months.
Nearly half admitted they do 10-20 per cent less work and an alarming 3 in 10 produced between 20-30 per cent less work in the festive month.
The reasons for this downturn in output includes a combination of exhaustion, lack of motivation and hangovers, said Avenance.
Other findings included six out of ten employees claiming they were less productive because they overindulged and ate and drank the wrong things.
Nine out of ten expected to attend at least four gut stretching Christmas lunches, which, at an average 2,000 calories per meal with all the trimmings, accounted for 80 per cent of the full day's recommended calorific intake for men, and the full recommended allowance for women.
Nearly a third said they would drink more than one bottle of wine with each work-related Christmas lunch.
One in ten blamed the consequent hangovers for their reduced output, with women being nearly twice as likely to be more hungover in December than at any other time of the year compared with men.
A third of the UK's workforce said they felt physically exhausted at the end of the year, with energy reserves too depleted to work as well as play.
One in ten employees admitted to having been ill over the Christmas break as a result of pre-Christmas over-indulgence.
Michael Audis, chief executive of Avenance, said: "Festive celebrations are an integral part of working life in December but businesses can do more to support their employees through what is a busy and stressful period of time on both a personal and professional level.
"This support is also critical to ensure that employees manage to stay well over the festive period and enjoy the holiday with their friends and family, as well as come back to work feeling recharged and refreshed," he added.
He continued: "These results show the role of food and drink in the workplace is now more than ever becoming crucial for the health and well being of employees and their productivity levels."
Festive fizzleout hit women harder than men, the survey concluded, with nearly twice as many women more concerned by Christmas than work compared with men by 14 of December.
Professor Chris Rowley, professor of human resource management at Cass Business School, added: "The UK economy cannot afford to lose £8 billion or work an 11 month year, yet companies continue to throw their profits away instead of making small investments for large returns.
"Many companies happily take their employees out for a Christmas meal but fewer invest in their workforce's well-being," he said.
"Rather than struggle against a burnt out unmotivated workforce in December, companies should consider taking small and simple measures, like providing cheap yet healthy foods in the workplace, or ensuring there are plentiful supplies of water in close proximity to workstations," he recommended.
"This will improve their employee health and well being, as well as productivity," he concluded.