An employee who is entitled to a flat rate expense deduction
under Section 367 ITEPA 2003 may instead request a deduction under
Section 336 ITEPA 2003 for the actual expense they incur in any
year. If an employee deducts his or her actual expense in one year
they are not prevented from deducting the flat rate expense in
other years. This is illustrated by example
In practice the most important advantage of a flat rate expense deduction to an employee is that he or she does not need to retain evidence to demonstrate the amount of expenditure they have incurred. Also, the amount of the deduction is calculated to be appropriate for the average employee taking one year with another. So high expenditure in one year may be balanced by low expenditure in another. For this reason many employees do not retain evidence of expenditure and do not request a deduction for their actual expenditure in those years for which it exceeds the flat rate amount.
If an employee does request a deduction for an amount of actual expenditure in excess of the flat rate deduction for any year it should not usually be permitted unless the employee has evidence to demonstrate the amount incurred, see EIM31715.