Further strikes this month will push the cumulative total even higher.
The number of working days lost since the current period of strike action began has passed four million, new figures show.
Some 4.1 million days are estimated to have been lost in labour disputes in the UK from June 2022 to June 2023 – the highest for any 13-month period since July 1989 to July 1990, when 5.0 million were lost.
Data for last month’s strikes by junior doctors, hospital consultants, teachers and rail workers has yet to be compiled.
Further strikes this month by doctors, consultants and rail workers will push the cumulative total even higher.
The figures have been published by the Office for National Statistics (ONS) and include provisional numbers for June 2023.
The present spell of industrial action kicked off in June 2022 when members of the Rail, Maritime and Transport union (RMT) staged their first stoppage in a dispute over pay, jobs and conditions.
It was soon followed by a sequence of high-profile strikes ranging from barristers, civil servants and university lecturers to postal workers, driving examiners, nurses and ambulance staff.
While many disputes have now been settled, some remain unresolved including those involving junior doctors and the RMT.
December 2022 saw the most working days lost in a single month during the current period of strike action, at 829,000.
This is the highest monthly total since November 2011, when 997,000 were lost.
It is also the second highest total since July 1989, when 2.4 million were lost.
More than half (54%) of the working days lost from June 2022 to June 2023 were in transport, storage and communication industries, according to analysis by the PA news agency.
This reflects the frequency of rail strikes, together with recurring disputes involving Border Force staff and driving instructors.
Nearly a quarter (23%) were to do with education, 11% health and social work and 8% public administration.