It occurred to me on the way home that the app I use to track my running might do more than I think. And lo and behold it's not as good as Saul's but it does show me in little graphs how fast I was running. So statistic loving me has just had a browse through the last weeks and made a few comparisons. The blocks of 5 minutes were faster than the 8 minute runs. And I did indeed speed up in the last minutes of the 8 minute runs, with the second 8 minutes being faster than the first. And I was running. Not fast, peaking at 9.2 km per hour this morning (9.5 on the 5 minute runs earlier this week), but still a darned sight faster than walking.
But first I have to build up stamina and get through W5R3. Looking forward to it now. Will provide more statistics to play with!