Sebastian leads me to a counter which is covered with different cups of tea from around the world, each one next to a pile of the tea leaves which were used to make it. Each cup is strikingly different in appearance - from thin and yellow to thick and red. The Tetley tasters have their own language, called Uhuru, which means freedom in Swahili, and Sebastian explains that they use it to score different teas. “We have four parameters, each of which is rated on scale of one to 100. What we call zing is the impactfullness of the tea on your tongue, its liveliness. How I think about it is, when you spit out the tea, how long does that flavour last? Then there’s colour, which ranges from very red to very yellow and everything inbetween.