The general principle is that where a driver holds a travelling appointment (as defined by EIM32366), or has to travel to a temporary workplace, his or her allowable travelling expenses include the cost of any necessary subsistence (see EIM31815). Guidance can be found:
This practice is based on the decision in Nolder v Walters (15TC380) and, in particular, on a comment of Rowlatt J on page 388, where he said:
'when you get a travelling office...the cost of [the individual's] food and lodging is not wholly and exclusively laid out in the performance of his duties, but the extra part of it is.'
In practice the full cost, not merely the extra cost, of meals is deducted.