Motorbooks, St Martin’s Court. Smack in the middle of a bunch of sites, inc. Leicester Sq, Traf Sq, Oxford St etc.

And from there head round the corner to Henry Pordes 58-60 Charing Cross Road. http://www.henrypordesbooks.com
He has a small but interesting aviation/military history section which also includes more Jane’s books than I’ve seen anywhere else, mostly recent. He has examples on his website to give an idea of expected prices.

Allan