I am not HMRC, but this answer is possibly wrong. The ACCA is shown on the List 3 of allowable subscriptions. Therefore if the individual pays their subscription for a relevant employment, it is allowable.
I am not employed by HMRC, but think this answer is completely wrong. Although the employer is not in the UK, the individual is still classed as employed and needs to account for their own Tax and (if applicable) NIC. This can be done by operating a Direct Payment PAYE Scheme or the tax can be collected via Self Assessment.
Any expenses allowable would need to be within the rules for claiming expenses as an employee.