Sorry guys, Ive made a mistake in my posts! The ball joints ive used are not Lotus Esprit ones they are in fact Lotus Elise ones, dont know why I typed Esprit!!
John, modifying the control arms does seem a good idea, so you dont need to play about with the diameter of the ball joint. However you would still need to machine in the groove for the cir clip and drill the shaft for the split pin. So work would still be needed on the ball joint.
Also, im hoping there will be a better long term solution to this problem from DMCH at some point in the future so I tried to avoid modifying my lower arms in case I ever get different ball joints.
I did use the retaining rings from the special T ball joints, they are simple to make up but at the time I didnt have the time to get them done so I just used the special T ones.