If you take on someone as a worker, the usual record keeping obligations apply. For further information see National Minimum Wage and National Living Wage - record keeping.
Work experience or volunteers: record keeping
If you provide work experience opportunities or employ voluntary staff, you should document the arrangement that you have made with the individual by keeping a record of any oral agreements in setting up the arrangements and any subsequent changes. In particular, if an individual claims that they are owed arrears of the minimum wage, the onus is on you, as the employer, to demonstrate that they are not a worker for minimum wage purposes and that no arrears of the minimum wage are owed.
The government encourages individuals who accept work experience placements or internships to keep records of what they agreed with their employer and this information may be used as evidence if their entitlement to the minimum wage is considered at a future date, eg by a tribunal or HM Revenue & Customs.
Note the promise of a contract or future job may amount to a benefit in kind which makes the individual a worker for minimum wage purposes. You can use the National Minimum Wage and National Living Wage checklist to help you decide if someone is a worker who needs to be paid it.