Good advice Paul F.
Morgan Cars Australia decided to fix the sagging springs on my new 4/4 by simply removing ONE of the lowering blocks.....
You can imagine what that did for alignment not to mention it was an illegal modification in my part of the world. The Feds got involved as the vehicle was not Australian Design Rules compliant with regard to ground clearance - I won't bore you with that story.
The blocks are not only a spacer but also a location device. IIRC, a stud in the spring locates in a hole in the block which in turn locates on the axle.
The only fix is new springs - in the UK Peter Mulberry (mulfab) 4 seater, 4 leaf rear springs are the answer. Worth a conversation with your dealer before committing - there may be a local solution that is easier for you to get. You definitely do not want MMC supplied springs as, depending on the age of the stock, you could easily be getting the same thing as you already have.
It took me two days to swap mine. A dealer might do it in 8 hours with their better kit and more experience of doing the job.
