This is a brief guide to risk assessments. The Health and Safety Executive provide more comprehensive guidance here.
A Risk Assessment is a list of Hazards that could arise from an activity, piece of equipment or a place and the control measures that will reduce the chances (likelihood or risk) of people being harmed by the hazard.
Generally, yes it is a sensible precaution but in some circumstances it is a legal requirement:
Employers, employees and the self-employed have a duty under The Health and Safety at Work 1976 to take precautions to prevent harm that might arise from their activities. This duty extends to volunteers where they are authorised to carry out activities on Council premises or are supporting a Council activity.
Voluntary groups generally have a common law duty to do what is reasonably practicable to prevent harm to others. If the Volunteer Group is an employer or responsible for non-domestic premises they may have a legal requirement to carry out a risk assessment.
If in doubt carry one out!
Voluntary groups might have someone with experience and training willing to carry out the risk assessment. If the activity etc is on Council premises or being carried out under the control or supervision of the Council then a competent Council officer should carry out the risk assessment or check any prepared by the group.
The Health and Safety Executive provide a useful form or there is a simplified form available.