Ive done a bit of playing around with a speed-distance-time calculator, and found that something is wrong with my memory off it.
I know that I was riding at 9mph after scrubbing a little speed off and I still had my fingers on the brake levers and that I was dragging the brakes lightly.
My estimate of 2.5 metres can't be correct.
If we are generous regarding my reaction time by calling it 1sec as I was fully prepared to drop the anchors, he must have pulled out when I was at least 8 metres away.
The highway code assumes 0.675 s reaction time. I think that includes the time taken to release accelerator and press the brake. If you were already dragging the brakes, and you had already considered the possibility of him pulling out I would guess around 0.3 s.
9 mph is 4 m/s, so that would only be 1.2 m
I would estimate 0.5 g stopping. Cars can manage about 1 g, and the highway code allows for 0.67g.
From 4 m/s, the distance would be 1.5 m at 0.5 g
Total would be 2.7 m
Obviously that figure is heavily dependent on the estimates for reaction time and deceleration, and the accuracy of the speed recorded.