Am I misreading this somehow? The guidance you linked to mentions volunteers thrice:
•all NHS and social care staff, including: •doctors, nurses, midwives, paramedics, social workers, care workers, and other frontline health and social care staff including volunteers
•frontline local authority staff and volunteers, including •those working with vulnerable children and adults, victims of domestic abuse, and the homeless and rough sleepers (and hotel staff supporting these groups)
•voluntary sector organisations providing substance misuse treatment
So its pretty bloody clear that volunteers are included where they are providing essential services during the lockdown and not anyone who has ever volunteered in any capacity.