Generally expenses are only tax deductible if they are 'wholly and exclusively' for the business. As we need lunch to survive rather than for our business it generally it is not allowable.

The exception is a reasonable expenditure on meals when on business trips. So if we visit the NEC for a trade show in Birmingham we can claim for food whilst away. What is reasonable is not defined but generally understood to exclude extravagant meals.

The question then becomes what we can consider a business trip. HMRC uses the idea that a business trip is something outside a 'normal pattern of travel'. A plumber's normal pattern of travel is to be out on jobs day to day and on those days buying lunch as a business expense would not be allowed.

There is also an exception made for itinerant workers such as commercial sales people or lorry drivers.

Entertaining clients or suppliers is never tax deductible.