The author’s viewpoint in this excerpt is that tea drinking, which is stereotypically seen as a quintessentially British tradition, is actually not indigenous to Britain at all. Rather, it is the result of Britain’s global trade and imperial history.
The author makes this viewpoint clear through several observations:

1. They point out the irony that tea, often seen as an iconic British drink, is made from plants (tea leaves) that are not native to Britain, but instead grown in places like India and China.
2. They note that tea is often sweetened with sugar from the Caribbean, again highlighting ingredients from outside Britain.
3. The author states directly: “It is one of the ironies of British national identity…that the drink which has become the worldwide caricature of Britishness has nothing indigenous about it, but is the result of centuries of global trade and a complex imperial history.”

So the author is challenging the perception of tea as a uniquely British drink or tradition. Instead, they argue that Britain’s iconic tea culture is actually the product of its colonial past, global trade, and acquiring ingredients/commodities from its empire and trade relationships abroad. The supposedly quintessential British beverage is portrayed as a byproduct of Britain’s global imperial reach, rather than something native to the nation itself.