Key bit of the article that is worth reading (unedited):

It wasn’t until 1784, when Richard Twining of the Twining tea dynasty persuaded William Pitt the Younger to reduce the tax on tea from an incredible 119 per cent to 12.5 per cent through the operation of the Commutation Act, that tea sales really took off.

This ended a century of punitive taxation which had turned smuggling into a major industry and greatly helped the East India Company – of which Twining was a director – in its lucrative trade selling Indian opium to China. It was paid in silver, which was used for buying tea.

www.onlondon.co.uk/vic-keegan-how-the-city-of-londons-tea-and-coffee-shops-bubbled-up/amp/