Lexus Derby (who use a local specialist) confirmed GBP240 inclusive of VAT. However, economic logic took over. As I was changing the tyres in any case I have committed to a set of aftermarket 18 inch wheels complete with the tyres that I prefer. These make the original wheels available for winter tyres which I can refurb at my leisure.
Regarding tyres I was quite interested in the Dunlop Maxx RT (very quiet @ 68dB) until I saw the poor wet-braking performance. Staying with the slightly noisier (71dB), but known Uniroyal Rainsport 3..