modified CIU look through method
40the method for calculating PRR for a CIU set out in BIPRU 7.7.4 R, BIPRU 7.7.7 R to BIPRU 7.7.8 R and BIPRU 7.7.11 R to BIPRU 7.7.12 R
40the method for calculating PRR for a CIU set out in BIPRU 7.7.4 R, BIPRU 7.7.7 R to BIPRU 7.7.8 R and BIPRU 7.7.11 R to BIPRU 7.7.12 R