Indemnity, Insurance, Volunteer, Work, Cover
We don't sell the indemnity insurance, so you'd need to get it elsewhere.
However, as long as you weren't being paid for the work, you'd be covered to carry passengers on a social basis (otherwise known as “giving your mates a lift”).
Just so you're aware, you'll still be charged for the miles driven during the volunteer work, even if you have other indemnity insurance in place.