Ichneumon and Braconid wasps can be rather frustrating insects to identify. First of all they tend to be very active and rarely stand still long enough for you to get a good photograph of them. Secondly, there are so many species of them, several thousand in the UK alone, that it can be difficult to know where to start. However, this morning, when I saw the white feet on the wasp in the above photo, I thought I might be in with a chance. A search for "White footed ichneumon" on Google lead me eventually to the Braconidae page at Watson, L., and Dallwitz, M.J. 2003 onwards. British insects. Version: 31st May 2009. http://delta-intkey.com, and this illustration of Zeles albiditarsus (also known as Zemiotes albiditarsus) in particular. The match seems pretty good: white 'feet', 'spurs' on the 'ankles', red on the right parts of the abdomen. I'll take this as a tentative identification.
Photo taken in Reading University grounds, Reading, UK, on 2009-06-07.