This situation is now resolved as follows
Williams Morgan could not source the ball joints, but do have the capability to extract the old ones and fit the new ones and Brands Hatch Morgan could source the ball joints, but couldn't fit them.
I have therefore bought 4 ball joints from Brands Hatch Morgan and will take them to Williams next week to fit.
The upper and lower ball joint are the same, so I have bought 4 and will keep them as spares.
