There are a number of ways of calculating a P/E. You can use the HEPS of the previous financial year, or the EPS of the current 6 months + EPS of previous full year - EPS of 1st 6 months of previous full year, or...or...or
According to my data on Brait:
Sep 12 Interim EPS - 242c
Sep 12 Interim HEPS - 242c
Mar 12 Final EPS - 654c
Mar 12 Final HEPS - 545c
Sep 11 Interim EPS - 491c
Sep 12 Interim HEPS - 346c
It seems FT.com is using the previous financial years EPS in their P/E calculation. However they have their EPS as 661c (compared to my data which is 654c). Not sure why there is a discrepancy