1 minute into the jog, I felt my hamstring / groin / buttocks. Tried to run through it for 30 secs but quickly got worse so called it a day.
I think it is a strain rather than a pull, so hopefully rest and ice pack will do the trick.
What I am pleasantly surprised by is how disappointed I was when it happened. Rather than thinking, "Well, that has saved me another 20 minutes of pain!" - I was actually gutted that I couldn't complete the run.
A silver lining perhaps...