Thanks for the replies folks - I'm (kind of) sticking to the Runner's World intermediate 5K schedule in preparation for the Flora Light in a couple of weeks and today's task was 10 min followed by a measured mile (hence the Regent's Park track question) followed by a further 10 min. Knackered now!
Does anyone experience stitch over the site of an operation scar? Any ideas as to why this might be and whether there are special ways (apart from the not eating not long before a run, breathing out when the opposite foot hits the floor, speeding up, and carrying a stone[!] suggestions) to avoid it?