It's 8am as we pull into the car park at Startop's End, squeezed between the reservoir and the canal. We are squeezing things in this weekend, ourselves. David is due back at lunchtime to watch the Spurs game and this is our only chance for a walk. It has to be short and local. In no time we reach the Aylesbury Arm of the Grand Union. A narrow and also straight canal, the original intention was to connect up with the Thames but money ran out and railways arrived...