Could this be a hybrid? Looking at Madge & Burn pl 35 and text 241 et seq the white on the flanks doesn't seem to be extensive enough for a pure RCP and the white on the wings is not typical as far as I can see. The primaries and secondaries should be white but not the tertials. The feathers also look very worn in the photo - abraded quite badly. Possible escape too? The Handbook of Bird Identification also gives similar descriptions but of course Steve madge co-authored that with Mark Beaman so not unexpected. Just my 3 pennyworth.
Andrew
