EIM31818 - Travel expenses: general: accommodation and subsistence: subsistence costs that are not attributable to the travel: examples
Example 1
For several weeks an employee performs duties of his employment at a temporary workplace close to his home. He chooses to stay in a hotel as he is having some decorating done at his home. The stay in the hotel is not attributable to his travel to and from the temporary workplace and so he is not entitled to a deduction for the costs.
Example 2
An employee who has to make a business journey takes a packed lunch that he has prepared from items purchased as part of his weekly supermarket shop. The cost of the packed lunch (even if it could be precisely identified) is not an expense incurred in the course of the journey and so is not attributable to the travel for the purpose of sections 337 and 338.