Hi, I think you have to be a bit careful about paying to cover things like meals and travel. You could allow them to claim back via your expense policy?
We have some students for whom they need to undertake an internship/work placement as part of their studies. On such a basis, they do not need to be paid the Minimum Wage but we tend to pay them in line with the minimum wage for their age. We also put them on payroll as casuals so they accrue some holiday entitlement and pay.
Worth noting also that if the student is on a Student Visa and the internship is an essential part of studies, then those hours do not count towards the 20 hour termtime max (but any other hours worked do).

In reply to Helen:

Hi Jeremy

Generally you must not pay fixed-sum allowances for 'expenses' - only actual out of pocket expenses.

Full details eg here
www.gov.uk/.../national-minimum-wage-work-experience-and-internships