Do you know if you need to pay an intern or a student on work experience? There is useful guidance on the Gov website to help you decide.
https://www.gov.uk/national-minimum-wage-work-experience-and-internships
The simple answer is that in most situations yes you will need to pay.
And there is of course a whole other debate about the moral position paying (or not) the people who work for you. We believe that if you want great employees whop give you their very best, then paying them a fair wage for the job done is really part of the deal. What are your thoughts?