Since 6th April 2016, certain job related expenses paid for or reimbursed by an employer to an employee are exempt from tax and NI, e.g., business travel; subsistence; entertainment and subscriptions. Under rules prior to April this year, employees, including directors, are taxed on expenses reimbursed to them but can then make a claim for a tax deduction for those costs incurred in the course of their employment.
Due to this change, it might mean an employee is entitled to a tax deduction under the old rules for expenses that are exempt under the new rules.
So, if incurred in one year and reimbursed in the subsequent year you can either:-
1) Continue reporting as previously to ensure no tax avoidance or
2) If, as is strictly correct, you have traditionally reported the expenses in the year they are reimbursed either a) provide employees with a note of what not to claim on this tax return as they have now been exempted i.e. if reimbursed in 2016/17 or b) tell the employee to claim a tax deduction on the 2015/16 return but there will be a corresponding tax charge in 2016 /2017 when expenses are reported on a P11D for that year.