OK I'll come clean
User3143 was almost right. It was for the Liverpool Marathon, the organisers wanted a couple of keen cyclists to help chaperone the lead runners around the course so I volunteered, we had to wear official reflective waistcoats with the organisers logo on the back. It was great riding on closed roads and not being told to get off the road by the police
When normally seeing runners go past I never think anything of it, but after riding the full course with them I now realise what an achievement it is, I take my
hat cap off to them. The runners near me were averaging 10mph, some cyclists struggle to do that on a bike.
Sorry for being mischievous, I see I got one or two bites