Have successfully completed this run....but goodness that was harder than it had any right to be! Thanks to Lee337 and to everyone who has posted about the pitfalls of this run. I don't understand why running a 5, 8,5 set of runs should be so hard, but I can confirm it definitely is!
I was willing Laura to tell me I'd got half way through the eight minute run so I could turn back round and head home...and then willing her to say I could stop running for the whole of the second four minutes!
At least I knew that others found it a real trickster, though, so I just slowed down, tried to keep calm and kept running. Knowing it was going to be hard and that was normal was a great help, so thank you all! And YAY I did it ! And nearly fell over the neighbours cat when I got home, but that's another story!