I don't know what went wrong. Well I do, my breathing was all over the shop. I got to about 18 minutes and just stopped. Which was another mistake as if I'd just kept walking for half a minute to recover my breathing I might have been able to pick it up again.
A couple of other tactical errors: I ran my route clockwise rather than my usual anti-clockwise which seemed to emphasise the uphill elements, and I was too warmly dressed. I bought a short sleeved top yesterday so I'll try that next time I go out.
Just lots of negative thoughts: you're too heavy, you're not cut out to do this, plus Laura's music was really p'ing me off this morning.
So, disappointing, and I'm a bit cross with myself. I was back on the flat when I stopped! Still, I ran for the second longest time I've ever run, and I'll have another go on Tuesday. I wonder if I should have a break from the programme for a week and try and build myself up to 25 minutes incrementally.