There is a quite a few threads on work and volunteering bubbling up.
So I thought I would post a link to the Disability Rights quite to "permitted work" and volunteering. I looked into this a few years ago and it was a nightmare even then. Now with the greater deployment of Universal Credit (UC) it is even more of an issue.
Whist before you may have been allowed to do "permitted work" on Employment and Support Allownance once you move to UC this isn't necessarily allowed.
Similarly volunteering opportunities may not be as straight forward as they seem. A volunteering role could certainly affect certain aspects of a PIP award.
Here is the link
disabilityrightsuk.org/work...
Hope it is useful