It is really very simple though. All you need to do is to read the information available on the website.
Apply for a Licence Conversion | Our Role | About the CAA
Use the online form available here and input the information as required.
https://apply.caa.co.uk/CAAPortal/te...t?formCode=PCO
but it doesn't state what ID is acceptable
Use the ID you use to carry when you go flying. It is mandatory to have an ID with your picture when at the controls of an aircraft. Use that ID.
There is also a tick-box that states: "I confirm that I have demonstrated the use of radio navigation aids to the satisfaction of Chief Flying Instructor which has been certified in my flying logbook." As the holder of a JAA PPL(A), this was demonstrated on my GFT, why is it now necessary for this to be annotated in my logbook by an instructor???
Send your English Language Proficiency certificate. That would suffice. If you are a UK native speaker, you don't need that.
WP