Just an update as the Japan Centre has gone through a period of refurbishment.
The website doesn't fully represent the range of green teas they now have available.
They've recently opened a department dedicated to tea and sake. This is located in the basement below the Toku restaurant.
The range of green teas is bigger than ever. There is even a small range of very reasonably priced wagashi.
Alas, only one tea is made available for tasting. However, some of the teas can be bought upstairs in the Toku restaurant. If you visit at a time the restaurant isn't too busy, I imagine they will be able to help you select a tea to drink that can be purchased from the shop.
Also of note is the range of tea cups/teapots/utensils that can be bought here (and in the grocery department next door - check both). There are some very nice cups available. Most are 1.50GBP (approx $3) some cost a little more.
Alternatively in London. If you'd like to try before you buy and have the tea made (and presented) perfectly then there's
(9, Dering Street - just off New Bond Street, London W1S 1AG)
A cup of tea here costs just 1.50GBP - a real bargain in London.
A small selection of sweets and snacks are also available.
If you like the tea enough to buy it, the cup of tea is complimentary/free.
This is a marvellous place to try and buy green teas from China and Korea and is an excellent alternative for Japanese teas to the Japan Centre.
Just don't expect fast service. Do
expect good advice from the knowledgeable staff.
A range of tea caddies from a long established Kyoto manufacturer is currently on display. The kind that take on a patina as they age. Absolutely beautiful!