Patrick
You can work for less for up to but not including 16 hours per week and earn up to about £102/week (check this figure as it may go up from Monday 6 April).
You need to ensure that any work you do does not conflict with your stated limitations, if it does then you risk your claim being re-assessed.
Have a look at our guide to Permitted Work for more information.
www.benefitsandwork.co.uk/help-for-claimants/esa1 Gordon