This is what the WOF book says :
LVV certification is not required provided that:
Springs and shock absorbers
-the springs or shock absorbers are direct replacements, and
-replacement springs fit and maintain contact with un-modified OE seats throughout
full suspension travel, and
-replacement springs are self-retaining in their seats at full extension, without the use
of non-standard devices such as wire-ties, straps, or external spring locators, and
-replacement springs have not been heated or cut, and
-springs and spring seats are not height adjustable (unless OE), and
-replacement shock absorbers fit un-modified OE mountings, and
-suspension maintains sufficient travel for safe operation when fully
laden, and
-suspension components maintain sufficient clearance from unmodified bumpstops
when fully laden, and
-a minimum of 100 mm ground clearance exists below any part of the vehicle
structure, or any steering, braking, or suspension component1, and
-the normal relationship between front and rear suspension height is not unduly
affected.
Lowering blocks
(for leaf springs,
to adjust their ride height)
the blocks are:
- securely fitted, and
- constructed from metal, and
- designed for the purpose, and
- firmly seated over not less than the OE seat area, and
- not more than 50 mm in height.