Its pretty straightforward. The ATO & your examiner need to comply with the latest EASA examiner differences document. They do the training complete the test notification procedure, and do the check then fill in the CAA paperwork, give you a copy, and email a copy to the CAA. They also need to send a copy of the examiner licence & medical, ATO accreditation, simulator certification ( if applicable). The examiner will not be able to make an entry in your licence for the skill test, so you will need to fill in the application form and send it to the CAA with the appropriate cash. Job done!
Dont worry, the ATO should know what its doing - I am a foreign examiner, and have done the same thing for most EASA countries over the last few years.
EDIT: DAMN, that crab beat me to it!