Hi Cath50t
Here is the guidance from gov.uk
Working while you claim
You can usually work while you are claiming ESA if both of the following apply:
you work less than 16 hours a week
you do not earn more than £195.50 a week
You can do as many hours of voluntary work as you like.
Tell Jobcentre Plus about your work including any volunteering when you make a claim.
www.gov.uk/employment-support-allowance/working-while-you-claim David