Earlier quoted context omitted.
No opinion on the quality of their tea, but Tea Pigs was the first brand which came to mind when I read 'plastic teabag': https://www.teapigs.co.uk/tea/shop-by-category/black/single-...
They claim they don't use plastic at all, not even for packaging: https://www.teapigs.co.uk/about/sustainability-and-values
EDIT: in fact, looking at this page[1], it seems they might be one of the only ones who do make a biodegradable bag ...
1. https://www.scotsman.com/read-this/is-your-favourite-tea-mad...