Then I realised. It's not a milestone. It's a brick wall and in gigantic letters:
From Now Till Eternity
No U Turns
I wasn't too concerned. It looked a long way off. If I kept it in my line of sight then it couldn't suddenly loom up in front of me could it? Will I never learn? They tell you not to rely exclusively on your SatNav don't they? Well, mine took me off the main road, down an embankment and into the icy waters. As I thrashed around trying to keep my ahead above water I noticed a sign on the river bank...