The number of sick days taken by British workers has fallen to the lowest on record according to official figures, as experts warn that many employees are coming into work when ill because they are fearful for their jobs.

The Office for National Statistics said the average number of sick days taken by UK workers fell to 4.1 days in 2017, a sharp decline from the 7.2 days recorded in 1993 when the data was first collected.

The sickness absence rate is 1.7% in the private sector and 2.6% in the public sector. Sickness rates in the public sector have fallen faster than in the private sector since 2008, and now stand only marginally higher than the 2.3% rate in big private sector companies with 500 or more employees.

The most common reason for a sick day is a minor illness, such as coughs and colds, making up 26% of the total.

Back and joint pain are the next biggest source of absences, particularly among 50- to 64-year-olds.

Among younger people, there has been a significant rise in the number citing mental health as a reason for absence. Among 25- to 34-year-olds, 9.6% of sick days were due to mental health conditions, up from 7.2% in 2009, the ONS said.

The TUC general secretary, Frances O’Grady, said: “It’s time to ditch the myth that UK workers are always throwing sickies. The reality is that people are more likely to go to work when ill than stay home when well.

“If someone is poorly, good employers will encourage them to rest up and get better. UK workers already put in billions of pounds worth of unpaid overtime every year. They shouldn’t have to battle through illness as well.”

The lowest rate of sickness is among private sector workers in the agriculture, forestry and fisheries sector at 1.4%, while public sector health workers had the highest absence rate at 3.3%.

The ONS said: “Rates may have decreased as healthy life expectancy has improved over time. Rates in the private sector could be lower as workers are less likely to be paid for a spell of sickness. There may also be an increase in presenteeism, where people go to work even though they are ill.”

Sir Cary Cooper, a professor at Manchester Business School, said presenteeism was the major factor. “Sickness absence is low because presenteeism is high. Given the aftermath of the recession and with Brexit looming people are frightened to be off ill, so they show ‘face time’ when ill or feeling low or job dissatisfied. They do not want high levels of absenteeism on their HR record, which they feel will make them vulnerable.”