Where is the best Tea Shop in Downtown London, UK

Silly for me to be answering this, as I don’t live there and haven’t been able to visit for ages. But, that said – last time my daughter and I went, we stopped into the Yumchaa tea shop (http://www.yumchaa.com/tresc//69/) in Camden Lock Market and it was fabulous. We didn’t go on a weekend, and I gather it can get pretty crazy, but it was nice and quiet and we love their teas. When I get back there, I’m going to try Postcard Teas (http://www.postcardteas.com/)too – I’ve never been in but have ordered a few times from them. Very serious tea merchants, but lots of good reviews for the teashop. And how cool is it to be able to post a postcard tea from the shop’s own mailbox? :) And finally, I gather Mariage Freres has a branch in Selfridges now, which I certainly wouldn’t want to miss! (MF shipping costs to Ireland are pretty awful.)