The survey shows that 60% of the nation’s convenience store retailers work more than 50 hours on average per week, while just 7% work fewer than 30 hours.
More than half claim to take less than 10 days’ holiday a year, while one in five takes no holidays at all.
The ACS said that Office for National Statistics figures put the average working week for most other professions at between 30 and 40 hours a week.
ACS chief executive James Lowman said: “You can add to these figures the many hours spent outside the store but working in the community on local events and initiatives.
“We know that 89% of local shops play an active role in the community, on top of spending every day engaging with customers behind the counter.”
The hours worked by self-employed retailers are far greater than the legal maximum working week of 48 hours for employees under the working time directive, which also stipulates leave equivalent to 28 days for full-time staff.