The general rule for employees: expenses: wholly and exclusively: apportionment: decided cases in which apportionment was permitted
The practice of apportioning expenditure where a definite part can be identified as incurred wholly and exclusively for a particular purpose has been approved by the courts.
For example, a similar “wholly and exclusively” rule applies to deductions for trading income purposes. In the trading income case of Caillebotte v Quinn (50TC222) Templeman J commented:
“It is possible to apportion the use and cost of a room on a time basis, and to allow the expense of the room during the hours in which it is used exclusively for business purposes, in the same way as it is possible to calculate the business expenses of a car which is sometimes used for business purposes exclusively and sometimes used for pleasure.”