I eventually got the tyres from ASDA Tyres - ordered online and they were delivered to and fitted by my local garage. Really good value - Pirelli P Zero J 255/35 R20 97Y fitted and balanced etc for £475.08 inc vat. Worth a go if anyone is looking.
I have the same tyres on my XJ (255/35 ZR20 97Y) and have just spent the morning getting prices on replacing the two at the rear. So far the best quote I am getting is £539.50 fitted from Kwik Fit (Pirelli), so I would be interested to know how much you paid, and if they are cheaper, where from? Thanks