Look at Table 1 of Page 3 to Section E of
http://www.caa.co.uk/docs/33/LASORS_06_WEB.pdf
You will note that any one holding an ICAO IR(A) is required to undergo at least 15 hours of training (including 170A) and pass the skills test.
As a CPL(A) is already held, there may not be a need to undergo theoretical knowledge instruction. However, also note page 7 to Section J detailing the theorectical knowledge acceptance period i.e. 36 months in which to obtain an IR(A) or face having to do them again.