The requirements for a CRE/IRR course are
Entry requirements (include)
Hold at least a CPL with the appropriate SE/ME SPA IR
A current UK/JAR-FCL unrestricted Flight Instructor Rating or Class Rating Instructor Rating valid for the Type/Class for which authorisation is sought
500 hours as pilot of aeroplanes
30 hrs instruction on the Type/Class required, not less than 10 hrs P-I-C in the previous 12 months
This is taken from the website of a company who provide flight examiner training courses at Bournemouth.
Linda Mollison