Agree with all the above, absolutely.
I've bought all my Nikon cameras and lenses at Grays of Westminster over some six years or so. I've only bought used bodies (D700, F6, F100) but the lenses have been a mixture of new and second-hand. I've not only been delighted with everything I've bought from them but I've also enjoyed dealing with them as a customer.
To my mind, for their used equipment they only deal in high quality items, and this and the reliable guarantee service they give accounts for the highish prices. I've found them worth every penny they charge. Also, they know, or can find out, nearly everything you need to know about things Nikon. Great service, as others have noted. And Gray and all the staff actually love photography and revere good equipment - it comes across when you deal with them. Highly recommended.
Incidentally, I believe that the owner, Gray Levett, likes Nikon rangefinders (he's written about them in the past in the Nikon Owner magazine, a high quality publication that the shop has good links with) and they've always got a good stock of them.
Gray himself is an interesting man, and the company is about to celebrate 30 years in business. Part of the celebrations include the annual Christmas Dinner. Their current advert has some useful information so I'll quote from it here:
"Our annual Christmas events are always unique, and this year we will be celebrating the occasion of Grays of Westminster’s 30th Anniversary.
Grays of Westminster, the multi-award winning, exclusively Nikon dealer based in central London, services the photographic needs of over 47,000 clients, including A-list movie stars, rock stars and royalty as well as people from all walks of life and professions. It is the first camera shop in the world to be granted a Coat of Arms by Her Majesty’s College of Arms.
The meal will be followed by an illustrated talk by Gray Levett, the founder of Grays of Westminster, as he tells us about the company he started with only £100 to its name, and describes, with anecdotes and stories, his extraordinary life of over four decades in the photographic business. It is a career that has straddled music, photography and the movie world in both the UK and Hollywood, encompassing legendary figures, such as Kate Bush, Art Garfunkel, Rod Stewart, Stanley Kubrick, Lord Snowdon, David Bailey and Terence Donovan."
It's got me tempted to go myself!