Four out of ten workers – approximately 4.5 million people – rarely use their full holiday entitlement over the course of a year, according to new research.

Hilton Hotels & Resorts commissioned a study of 2,000 employees and found that the average Briton gets 23 days of leave every year.

Forty per cent of the workforce rarely or never use their full allocation, while 15 per cent have at least six days outstanding at the end of most years, according to the survey.

The most common reason for failing to make the most of holiday entitlement was simply running out of time to use it, cited by a third of respondents.

A fifth of workers said they were too busy to take any time off, while one in seven (14 per cent) were concerned about the risk of losing their job.

One in ten employees said it was frowned upon to take the full amount of annual leave in their workplace.

Other reasons given for failing to make the most of holiday time include difficulties fitting in with colleagues' workloads, meeting schedules and days off, and simply not wanting to take that much time off work.

Companies using staff rostering software and other tools to get the most out of their workforce were advised to encourage employees to take regular time out to "recharge their batteries".

Behavioural psychologist Jo Hemmings said: "Taking a break from work and enjoying a holiday helps workers both mentally and physically, which really improves their productivity when they go back to work.

"Holidays are absolutely essential to our emotional wellbeing, providing time away from everyday pressures and deadlines. Quality time spent with friends and family, rest and relaxation and a change of environment all contribute to positive health and happiness."

The study also urged workers to try to switch off when they are on holiday, with a quarter of respondents admitting they call into the office to check up on things during periods of annual leave.