Employees have rights such as the right to a minimum wage because they are financially compensated and have entered into a contract. Volunteers, however, are not under a contract and do not have access to the same rights.
Usually, charities or voluntary organisations offer an agreement even though it is not compulsory. However, having a volunteer agreement and policy may show that a charity is serious about caring for volunteers.
The agreement expresses the relationship between individual volunteers and your organisation. A broader volunteer policy will detail how you manage volunteers across your organisation and outline processes and procedures relating to current or potential volunteers.