Since the introduction of Self Assessment in the 1996/97 tax year, employers have been required to calculate cash equivalent values of benefits provided to employees. Up until the 2016/17 reporting year they then had to perform the £8500 test to decide whether it is appropriate to return a P11D or a P9D to their local HMRC PAYE office by 6th July following the end of the tax year in which the benefit/expense was provided. The form P9D has been abolished from the 2016/17 reporting year.
Employers also have to provide copy information to their employees of the information sent to HMRC by the same date. This is so the employee can use the copy of their benefits information to complete their Self Assessment tax return if they were in receipt of one.
Finally employers are required to report changes to company car allocations to employees on a quarterly basis using the P46 (car) form.