OK, so
installations before the 12/12 will almost certainly be 43.3p until 1 April, and 43.3p after 1 April.
installations between the 12/12 and 3/3 will almost certainly be 43.3p until 1 April and will almost certainly be at least 21p but may be 43.3p after 1 April depending on the court case
installations between the 3/3 will almost certainly be 43.3p until 1 April, and will most probably be 21p after 1 April depending on parliament approval.
I'm glad it is all clear now!