Thanks for the ID. The leaves of this plant illustrated in Rose are much more heavily lobed than those here so I doubt I'd have ever got it myself.
agree your leaves not very typical, but hairiness and flowers give it away
I look for those bracts; irregular, adpressed, a central row of prickles growing darker towards the tip, purple at the tip.
Lat/Lng: 51.546948873781, -0.32630681991577
OS grid ref: TQ161844
Horsenden Hill nature reserve (http://www.ealing.gov.uk/services/leisure/parks_and_open_spaces/find_a_park_or_open_space/perivale.html)