The survey of around 1,000 members also found that more than three-quarters of respondents report regularly working late, either in the office or at home.
Managers report pressure to work these extra hours – with around half (53%) saying their workload is the main contributor to working overtime.
The main tasks adding to longer to working days were catching up on emails (78%), reading papers and documents (32%) and dealing with urgent or time sensitive matters (30%). While some admitted this pressure was self-inflicted, 44% said they felt direct pressure from their line manager.
Nearly half of the respondents (47%) polled work at least one additional day (7.5 hours or more) of overtime per week.
Charles Elvin, chief executive of the ILM, called the extra hours culture in UK business “widespread”.
“Excessive hours are not sustainable – there are only so many times you can burn the midnight oil before your performance, decision making and wellbeing begin to suffer,” he said.
“This is why it’s so important for organisations to equip staff with the fundamental planning and time management skills they need to cope with their workloads more effectively.”