The University of Dundee encourages students to engage in extracurricular activities. This helps to develop transferable skills and can give you valuable experiences. Such engagement is recognised by the Dundee Plus award.
The Home Office makes a distinction between volunteering and voluntary (unpaid) work. As a Tier 4 student, this is something you need to be aware of. Any time spent doing voluntary work counts towards your allowed number of work hours in a week.
The organisation offering the volunteering role should be able to tell you if it can be viewed as unpaid work or not.