animmo
You're right, the route was out by the width of a house or two. I've corrected the course of the alley's route based on a survey.

The position of the buildings don't match the Bing imagery all that well (especially the Swilgate Road buildings), so for now, I've matched the course of the alley to where the buildings are, ignoring the imagery.

If the building positions are corrected in future, the alley can be repositioned then.