We've rummaged in the archives, asked around and have been taught a thing or two by the building itself
The brick areas on the south face break up into 4 main areas: the medieval watermill, the old mill house (single storey), the floor added above the mill house and the infill between the two old buildings. The section of infill between the two straight joints is of precise English bond up to the ground floor window heads, but then it changes to irregular Flemish bond. This indicates that there may have been a bridge and a road between the two buildings such that you might drive a horse and cart through.
The picture below reveals the old timber frame structure that has been absorbed into the current building. You can see where the former outbuilding was and the gap between the two. Compare this timber frame structure with that of Ford End mill.