Crockatt & Powell are Adam Powell and Matthew Crockatt, two refugees from chain bookselling who decided they knew better than anybody else. There are two shops, one on Lower Marsh by Waterloo station and one on Fulham Road by the Chelsea and Westminster hospital. Here are the opening hours and a few pics of both:

Opening Hours Lower Marsh Monday 10-6 Tuesday -Friday 10-7
Saturday 10-6 Fulham Road Monday 9-7 Tuesday 9-7 Wednesday 9-9 Thursday 9-7 Friday 9-7 Saturday 10-7 Sunday 10-7