I wouldn't recommend Nicholas Camera, don't really have a good impression and experience, but I highly recommended Aperture.
My experience:
I went there from Edinburgh intend to buy a Leica M film body last month, looking for a M6 or TTL, I can't decide between the two and would like to get my hand on both. I went to Nicholas first due to their large stocking on website, but I was totally disappointed when arrived, the only M6 body they had on the day is in the warehouse, and only willing to get it for me if I am determined to purchase.
The shop was under reorganization at that moment, and they surely have a large collection from film SLR, Medium Format and Large Format in the shop, but not the M body I was looking for. Their listing on website is not entirely accurate, better to phone before visiting.
Then I went to Aperture, I got a chance to play with M6, TTL and MP, and the asian guy explained to me patiently the difference and what he thought, and thier stocking on website is updated accurately. In the end,
I went back to Edinburgh happily with M6 TTL .85, utterly satisfyed.
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Anyway, here are some of the dealers I had found on Internet not being mentioned before, I had only deal with Kingsley Photography on Tottenham Court Road which is a nice little shop, but may have limited Leica gears.
Richard Caplan deals with Leica and Ricoh
http://www.richardcaplan.co.uk/about.aspx
R.G Lewis, also another Leica premier dealer, they have mostly new rather than second hand stuff.
http://www.rglewis.co.uk/index.htm
Kingsley Camera on far end of Tottenham Court Road also have limited Leica Stock, also sells Nikon DSLR/Lens
http://www.kingsleyphoto.co.uk
Cheers,
Lucas Kao