Thanks SimonH, Good background and history. Thank you for posting.
However in the original posters case I would be tempted to simply remove the lowering blocks ( this may need new U bolts) and see if the increase in ride height cures the issue
Certainly a cheaper option than new springs
Simon @ SiFab.co.uk
That suggestion was made with my car but it was pointed out that if the original springs were from the dud batch as were mine as well as the second set Morgan provided then you are just hiding the problem. Both cars were built at the time of the "Spring Sag Issue" so that is a distinct possibility given that other cars delivered in Australia suffered as well.
It would be interesting to measure the side to side difference in ground clearance.
New 4 seater springs have solved my problems.