You do not have a contract of employment as a volunteer, so you do not have the same rights as an employee or worker.
You will usually be given a volunteer agreement that explains:
the level of supervision and support you’ll get
what training you’ll get
whether you’re covered under the organisation’s employer or public liability insurance
health and safety issues
any expenses the organisation will cover
The volunteer agreement is not compulsory, but sets out what you can expect from the organisation you’re volunteering for. It does not form a contract between you and the organisation.
The National Council for Voluntary Organisations (NCVO) has information on volunteers’ legal status.