that sounds really frustrating Lorraine,
I'm not quite sure if "access to work" covers voluntary work but i do know all organisations with employees are responsible by law for health and safety so a risk assessment could have been looked at to resolve concerns and not made u feel unneeded.
As its only a fill in manager perhaps u can speak to usual manager about this?
I wouldnt want to work for that one tho'- doesnt give u much heart, she doesnt sound very understanding at all,
Direct gov is useful site and has lots info about voluntary work, maybe learn more about your rights from here, hope this link might be helpful?
http://www.direct.gov.uk.../Volunteering/DG_064299
Take care Lorraine, dont be too down ~ i think we all have some stories / experiences of these kinds of unhelpful attitudes,
Remember, it's not us, it's THEM!
Chin up xx Love Liz xxx