I had both rear air shocks with after market ones about 4 years along with the wishbones. The work was carried out by the Jag dealer here and all has been well. Due to the upper bushes on the front shocks had deteriorated I changed the front shocks with same after market type but now the suspension is rock hard. What have I done wrong?

First of all what car jaguar do you have, please add year and model to your signature.
Do you have OBD reader that can read Jaguar codes including suspension height? If yes, any codes?
Did you replaced front shocks yourself or you had a shop do it? Regardless was suspension calibrated with SDD after shocks were replaced?