Hi Philip Staines,
You should complete P85 when you leave the UK providing all details regarding your departure from the UK.
If you are continuing to be paid by a UK employer we will consider if a code of NT (No Tax) is applicable.
You cannot do this in advance and should send the form upon your departure from the UK.
If you are not resident in the UK then a Self Assessment record may not be necessary.
We will review this in accordance with the information provided on form P85.
Please contact our National Insurance helpline on 0300 200 3500 regarding your national insurance.
Get your Income Tax right if you're leaving the UK (P85)