I was lucky enough to work at The Pattern Room in Nottingham for 5 weeks in 2003 (no longer there, sigh). I got time to visit both Holland & Holland and Purdey. I can tell you that when you actually handle either one, the price seems to be fair when you consider the work and quality. The samples I handled were amazing in every detail. The English scroll work engraving is beyond compare (for me anyways), the walnut spectacular, and the fit & finish is incredible.
That said, after visiting Piotti in 2004, if I was ever going to order a bespoke shotgun, a King grade Piotti is what it would be.