If your in the UK the there's a good chance that you've bought something online from Yogamatters, whether books, a mat or whatnot.
Turns out you can also visit.
I finally managed to make the trip one afternoon after the Richard Freeman class and must have spent two hours or more, in what is surely the biggest Yoga bookshop in the UK, possibly Europe (unless you know different ).
It's basically a small warehouse unit on a small industrial estate. VERY easy to find, perhaps ten to fifteen minutes walk from the train station.
Our address is 32 Clarendon Road, London N8 0DJ. We are short walk away from Turnpike Lane underground (on the Piccadilly Line) and Hornsey British Rail stations. There is ample free parking outside our units and bars to lock up bicycles.