Done it! Ran from my hotel to the west side of the Islington Tunnel, then went as far as Regents Park, did a very short cicruit in Regents Park then ran back.
All went well except my gps ran out of juice so I'll go on mapometer later to work out how far it was. Really nice place to run, but I have to say that none of the runners I met seemed inclinedto acknowledge my presence in the slightest - that's London I suppose.
Re the croissant/full English decision: I had a banana from Tesco Express on the way back, then porrige and bacon on toast.
First time I've run on a work trip and will definitely be doing it again, It set me up brilliantly for the day.