A typical cup of black tea contains 40-50mg caffeine per cup, but this will obviously depend on the strength of the brew.
Green tea has less caffeine than black teas as it does not need as long to brew, however, it still contains caffeine.
The only decaffeinated teas that we offer are the Earl Grey and Royal Blend Teabags:
https://www.fortnumandmason.com/earl-grey-classic-25-decaffeinated-tea-bags
https://www.fortnumandmason.com/royal-blend-decaffeinated-25-tea-bag-box
However, all the infusions are caffeine free (including the seasonal Plum, Apple and Cinnamon Infusion, 50g) and 4 out of the 6 of our botanical infusions are caffeine free (the two that are not decaffeinated are the Tempo and Grace).