Let's hear it from our new crowd, do you have a reliable corner shop supplier or perhaps you order online? Maybe Sainsbury's has all you need, I'd still love to know!
I treat myself to a few quarter-pound bags from Chicago's Rare Tea Cellar twice a year. I get a lot of loose-leaf teas as gifts, as well. My two "daily drinkers" are the Wagh Bakri Masala Chai which I get in a 100-bag box up on Devon Street (the Indian / Georgian neighborhood in Chicago); and a fujian tea that I identify by it's bright red box, which I get in either Chinatown or the Korean grocer nearer my house.
I'm also partial to Czar Nicholas ][, but I don't make a point of always having some on hand.
I've personally found gillards of bath to have the best tea I've found. It's well worth the cost. They supply a lot of the high end tea shops in bath, though often even they don't do the tea the justice it deserves. You need to prepare it properly. It's good enough that the weird little things can matter. E.g. warming the pot, or the difference between brewing and stewing it.
Their Three Gardons Ceylon is my favourite. Though their Earl Grey is also VERY good.
I can tell you where I was buying it: T2.
Then the bastards shut all their shops in the UK, leaving me with nothing but the 15-odd boxes of tea I still hadn't finished.
Man, I'm out in bumfuck nowhere in the Appalachians. If it ain't on amazon, I would have to drive to another state for the closest tea that isn't Lipton or Tetley. As much as I despise amazon, there's some things you just can't get reliably out here with anything else.
Like, there's plenty of online tea sellers. But getting the actual tea here is annoying as fuck. Lost packages abound, it can take a month to get here, by which time it's going to have issues. Sometimes it just isn't worth the fight to use some other retailer, especially if they don't have one of my preferred brands and I'm having to hope I like what I order. It ain't like I'm not on a fixed income, so having to choose between shitty tea that is a waste of money if I don't drink it, and dealing with amazon, that's what I choose.
Which is tangential, but sometimes I need a rant lol
I'm mostly living in the green tea world, so Ippodo and Den's Tea are my go to. They both have some darker tea offerings, like fermented Puerh or Oolong. Mostly looseleaf. I'm not very in the know, but they both seem to be good suppliers.
Mostly I buy from Yuuki-Cha.com for organic Camellia sinensis Tea in a Japanese style, and Japanese teaware. And for other herbs, I search the world over for good quality, and reasonable prices.