Out to lunch

I have several clients who are independent management consultants (some of whom are self-employed and some who operate through the medium of a company). IR35 is not in issue.

They all operate from offices in city centres and will usually buy a sandwich from a local takeaway at lunchtime. During the course of their work they will travel across the country (and occasionally abroad).

I have no difficulty in treating overnight and dinner costs as deductible (either from trading or employment income).

However what about any costs incurred on buying a sandwich at lunchtime when away from the office?

Common sense suggests that because they are incurring no greater expense than they would if based at their office no deduction is available. However I am sure (but cannot now find it) that HMRC manuals suggested that such costs were allowable for itinerant trades.

Am...