Woolworths?
Tea bags aren’t widely viewed as an abomination. Tea purists prefer loose tea, but the majority of the tea market is tea bags. I’m looking for some comparative figures of tea bags versus loose tea, and coming up slightly short at the moment. I’ve found a claim that 90% of tea drunk comes from tea bags, and although that rings true to me, the article does not cite supporting references. I can say that over 100 million kilograms of tea bags are sold in the UK each year.
I remember a Graham Greene quote, from “Travels With My Aunt” if memory serves, where he’s at a restaurant on some Caribbean island and observes an American at the next table removing a bag from his cup “like a drowned animal”, at which point observer feels “very far from England”.
Of course, it’s not Greene talking, it’s the narrator 
I agree that the method is a bastardised version of real cafe or railway tea where the pot was, as you say, warmed, then loose tea added before filling from the urn. Kind of like the woman who cuts the end of the leg of lamb because her mother did. And she did it because her mother did and grandma did it because the “baking dish wouldn’t fit the whole leg.”
However it isn’t true that the absence of boiling water makes infusion impossible. Tea will infuse even in cold water, it just takes longer. The recent trend towards flavoured black teas is a throwback to “sun tea”. I find that when making iced tea you can create a more delicate liqour by using long cold water infusion.
As don’t ask says, tea will infuse in other-than-almost-boiling-hot water.
There are a variety of constituent chemicals in tea, each of which infuse at a different rate… and these rates vary with temperature. “Sun Tea” usually has a more delicate flavor because the infusion rate for tannins drops like a rock with temperature. The resulting tea should have very little bitter or “dry” character.
It’s also why the first cup of tea generally tastes better than tea that’s sat in the pot. The aromatics infuse quickly while the tannins take longer (even in hot water). As you pour cups you’re drawing off the aromatics in solution (which are not being replaced as quickly over time), they’re being driven out of solution by exchanged with the atomosphere, and the remaining tea in the pot is continuing to leach tannins. Try it some time, brew two pots of tea, but start one a couple minutes later. The first cup poured at three minutes will taste different than the first cup poured at five minutes, all else being equal.
Teabags are an abomination if they contain low-quality tea dust in packaging open to oxygen. You might as well brew up a cup of dirt. However, they do offer the ability to control the infusion process, so you can avoid having to drink bitter lukewarm tea if you can find some with higer quality tea (or make your own teabages from cheesecloth and loose tea).
If the shelves at a very middle-of-the-road Tescos can be assumed to be representative of ‘normality’ (lets face it, their market research is better than we could manage), then the loose tea market is somewhere in the 5-10% bracket.
Being American and thus far removed from whatever class squabbles the Brits may have, I nevertheless add the milk after the tea for precisely the reason Mr Orwell suggests – it’s easier to achieve the ideal mix/colo(u)r if you add the milk after the tea. If you use teabags in your mug, I recommend letting it steep first, taking out the teabag and then adding the milk.
I do put the sugar in first, though. Again – it’s easier to measure. I’m just funny that way.
Anybody who puts milk anywhere near non-complete teabag-tea deserves a slap with a rancid kipper 
I’ve never understood the appeal of milk in tea. It makes it all…oogy tasting. It must be hot, very strong, and possibly sweetened.
And this godless American heathen has more than once sent a Brit into a fit by doing the following:
Take a cheap teabag - such as Lipton makes.
Place teabag in mug. Fill mug with tap water. Microwave mug for a minute or so. Drink tea. Watch the horrified looks grow. 
(Note: I’ve stopped doing that since I got a hotpot in my room, though it’s a pain to get water hot enough at 7500 feet…)