'Sustaining Communities: Taking the Strain' asked 3,688 local government workers about their pay and conditions, including how many hours they worked each week for which they were not paid or did not receive time off in lieu.
Thirty-four per cent of nursery nurses and a similar number of teaching assistants in England said they worked up to four hours unpaid a week.
Twenty-three per cent of nursery nurses, and 22 per cent of teaching assistants, said they worked between four and ten hours extra a week.
The survey also found that 13 per cent of the nursery nurses and 17 per cent of the teaching assistants surveyed were holding down two or more jobs.
As an occupational group, only chief officers in local government do more unpaid overtime than school staff, the survey found.
Only 32 per cent of nursery nurses said that they did no unpaid overtime at all.
Christine McAnea, Unison's national secretary for education staff, said, 'We have known for many years that school staff do a substantial amount of unpaid overtime. When you take into account that many of these staff work part-time and are low paid, their unpaid work constitutes a huge percentage of their working week and pay.
'Quite frankly, the goodwill of support staff is being exploited by schools and local authorities who depend on their commitment to get the job done without paying them for the hours they actually work. These results confirm our view that workforce reforms are slow to deliver tangible benefits to school support staff. It is becoming increasingly obvious that school staff pay and conditions need to be reviewed and overhauled.'
The findings suggest that local government workers are under increasing pressure to work longer hours, often without pay or time off in lieu, to cover for staff cuts and shortages. Fifty-seven per cent say they feel that morale where they work has got worse during the past year, and more than half of the survey's respondents believe they are not paid fairly for the jobs they do.
Nursery nurses and teaching assistants were also more likely than other local government workers to feel unfairly paid - 71 per cent and 72 per cent respectively. Sixty-six per cent of nursery nurses said their workload had increased over the past year and 59 per cent reported increased stress levels during the same period.
A Unison spokesperson said the findings showed that 'the trend' for unpaid overtime by support staff was not changing. Another survey carried out by Unison two years ago, 'All work and no pay', found that nursery nurses worked an average of 4.5 hours extra a week.
On the basis that nursery nurses are usually contracted to work 32.5 hours a week, the spokesperson said, this equated to a loss in earnings of 18 per cent a year.
