IIRC, to become a 'BX' examiner in the pre-JAR-FCL days, one either needed 1500 hours instructing or 1000 hrs plus assessment?
If you become an examiner, do remember that you will not be able to examine people you've instructed (apart from progress checks or safety checks)......
I understand that the CAA is now taking a closer look at the required number of examiners in any regional area - so there may have to be proven need rather than personal aspiration in order for someone to become an authorised examiner?