Yes. If the claim is wholly and exclusively for business purposes and your friend is working away from the normal "office", then they can claim subsistence.
For example, if I am working from my office, I can't claim for my lunch but if I go to visit clients and am out of the office for the day, then I can claim subsistence. Although, in the office, tea and coffee is claimed under staff welfare.
Receipts are always good - especially if VAT is concerned.