Winston -
If the ATPL is current (as you say) - then it's just a PPL Renewal flight test.
Use
this form - complete section 2B - and give it to the nice people at Gatwick.
Examiner should keep a copy of
this other form .
Examiner signs licence renewal - immediate.
Cool Hand - you give fewer details!!
Most likely same as above but (if more than 5 years 'expired') form sent to CAA for THEM to sign licence renewal.
Enjoy the return to G.A.