I can't believe I feel so different after the second run of my first week. For anyone else who is a newbie and found the first run a challenge, don't be put off....
My face still looks like it has taken the stain out of a beetroot, but I completed the last two run sections this morning without having to push through them as I did on the first go.
Thank you DiscoRunner for the advice on the Japanese slow running technique. I'm a long way from getting it right, but it certainly made me think about how I'm placing my foot.