Alignment round Sheepmarket seems to be a hot mess. Using OSM UK Cadastral Parcels layer, these parking spaces seem to be a good reference point for the aerial imagery: small, boundaries easily visible from aerial (I'm looking at Bing) and no parallax (?) from buildings captured from an angle - they're just flat at ground level. (Using these as a reference point I was able to make other parcels match the imagery pretty well.)

Who knows how it all gets sorted out, if at all: multiple land-use areas stitched together with other features is a complicating factor; the other is that these close-packed Georgian buildings make a tissue of ways and areas that aren't easily dealt with in small sections.