All the information you need is in LASORS, the Flight Examiner Handbook and the relevant CAA Standards Docs for the licence or rating course you are instructing/examining.
This will remain the case until 1 July 2012 after which an examiner may not, under any circumstances, test any applicant to whom he has provided flight instruction for the licence or rating - the national Authority will no longer have the ability to make any exceptions. This will, as now, apply to skill tests and certificates of competence but not to proficiency checks