The Xpower lowering springs from MG Sport and Racing days have been recommissioned and are now available ! The springs were originally developed by the MG Rover chassis engineers who now run Vehicle Handling Solutions and they are made by the well known automotive  spring manufacturer, Eibach.
They are suitable for 2.5 KV6 and diesel variants.
 
By design it should lower the car by 15mm. However, there is a +/-10mm tolerance always quoted by MG for the build and we should also remember that the car might be sitting low if it has old/original springs. The original factory ride height spec (wheel centre, vertically up to the wheel arch eyebrow) should be 345mm front, 353mm rear. The Xpower springs should then lower it 15mm from here.