Good plan Arctic. I ended up having to buy expensive springs. My car needs Orange RG coded rear springs and I could only find them at Rimmer Brothers or from a reseller on eBay for £115.
I'm not sure if they're OEM springs buy they should be, given where they came from. The label on the box says:
1x RKB000890SLP
Made in Germany
011a2 SUP01
Colour Code: 1x orange, code "RG"
0518
The great news is that my car passed the MoT with no advisories - I'd dropped it off earlier in the day with my bike in the boot so I could cycle off and return later. I got back to the MoT centre to find all the MOT testers having a fag, leant against the front of my car so as I unlocked it with my spare key, so I could put my bike back in I said "comfrotable is it?" - they were most apologetic and gave me the test for £20. Job's a good 'un!
It also feels a lot better suspension-wise at the back end. I should have sorted it a lot earlier.
Cheers all