Great Britain and Ireland (And miscellaneous former colonies)
There's a reason the poster children for the Spot of Tea trope are the British. The British demand for tea drove, among other things, the monopoly of the uber-powerful Dutch-style British East India Company, and the 1840-42 and 1856-60 Opium Wars. The media portrayal of the Brits as tea crazy pales next to many of the real life accounts. No shortage of British writers, including George Orwell [1], Douglas Adams [2], Neil Gaiman and a panel of British scientists [3]note , have written essays on the subject of proper tea prep.
Less Laconically: In 1660, King Charles II of England, Scotland and Ireland married princess Catarina de Bragança of Portugal. Part of her dowry was the Portuguese outpost at Bombay, which was sold in turn to the English East India Company. Consequently, ever greater quantities of tea and textiles were imported directly to Britain from India and China. By 1750 the British had fallen in love with it.
As a late-comer to the transcontinental trade, the East India Company had to make do with the proverbial scraps left over from the Portuguese, and then the Dutch (the world's great merchant-shipping power in the 17th century). However, Dutch supremacy could not last forever, and it was in the field of textiles and tea in particular that their early advantage counted against them. The Dutch had moved, ruthlessly, to monopolise the supply and transportation of spices, which were quite easily the most valuable goods to be found out east. However, the demand for spices proved limited; people can only eat so much of them, and their value eventually went down as the European market became saturated. On the other hand the British, having invited a Dutchman over to... kind of... be King in 1688, and having borrowed the modern Dutch financial system lock, stock, and barrel, and having made a few small but significant improvements on it (particularly, the invention of modern shipping insurance), and having gotten over their political troubles, managed to get enough money to exploit an unnoticed niche in the market: they would realise and capitalise upon the elasticity of demand for cotton and silk clothing (leading directly to the catastrophic collapse of the British wool-textile industry). And—of course—tea.
By elasticity of demand, we mean to point out that people are more willing to buy more of certain things than others. You can only buy and maintain so many cars, for instance. But there really is no upper limit, comparatively, to the number of music-recordings you might amass (especially these days). What this means in economic terms is that a small change in the price of a product with a high elasticity of demand will change the amount demanded a lot—reduce the price a bit, and a lot more people will start buying it (and/or people already buying the product will start buying more), but if you raise prices, the reduction in quantity demanded by consumers will be just as drastic. Because small reductions in price lead to large increases in quantity sold, a producer of a product with a high elasticity of demand will tend to try to maximise profits by selling more stuff at a lower price (if you can sell 10000 pounds of tea for 3 shillings per pound, or 30000 pounds of tea for 1 shilling sixpence per pound—which is three times the quantity at half the price—which would you prefer?note ). That is what the East India Company did with tea. What happened as the supply of Tea increased and the prices of it dropped is that it appealed to an ever broader (and relatively poorer) base of people. Consequently, the East India Company tentatively tried to see just how much Wulong tea they could flood Britain with before it became unprofitable. They were not disappointed. In Britain at least, by the 1750s it was already a recognized national drink. Interestingly, a significant upswing in health followed as people began boiling their water before drinking it. However, it was not until the latter half of the 19th century that people commonly took their tea with milk. This is because Wulong tea was cheaper, more widely available and highly regarded until about this time - when British investment in Indian plantations (which produced darker and more astringent teas) began to pay off. The transport and investment networks (i.e. railways and banks with the money and willingness to invest in pithy local business ventures) required to transport fresh milk to the Metropolises simply didn't exist before then anyway.
How they drink it: Black, hot and in large quantities (typically using teabagsnote ). Adding milk is common, and there is an ongoing holy war as to whether the milk or the tea goes into the cup first. Some people avoid the debate altogether by squeezing lemon into it insteadnote . It is entirely possible to divine a Briton's class, upbringing, and even politics, based on the way they drink tea. The mid-afternoon light meal called "afternoon tea", with sandwiches and scones and its precise etiquette, is a product of the upper-middle classnote (not to be confused with the evening meal, which working to lower-middle class people call "tea" rather than "dinner" or "supper"—even more confusingly, this working-class "tea" is what upper class Brits call "high tea"; high just meaning later in the day/eaten off physically "higher" dinner tables as opposed to the "low" tea tables to distinguish it from afternoon tea), while lower classes stick with a cup of tea and a snack. "Builder's tea", the staple of the working classes, is cheap tea brewed extra strong with a generous amount of milk and sugar (jokingly, an amount sufficient for the spoon to stand upright in the mug). Earl Grey, invented in China, named after The Earl Grey, who received a shipment of it as a gift, is tea flavoured with oil of bergamot, a bitter citrus fruit, and in some varieties with added orange or lemon peel, or with various flowers such as lavender, verbena or rose petals. "English Breakfast" and "Irish Breakfast" are both popular named tea blends, but the actual teas included in them vary; what matters is that they're strong, hearty concoctions that can stand up to the English/Irish full breakfast of eggs and fatty cured meats.
Also: as you might have understood from the above, British patterns of tea consumption are largely replicated in Ireland, with some minor differences. Indeed, the Irish are, if anything, even more tea-crazy than the British, consistently consuming more tea—by weight—per capita than the British do.
During WWI the British used water cooled machine guns. British soldiers would sometimes fire off hundreds of rounds just to heat up the the water inside the cooling jacket of their machine guns so they could make tea.
During World War II, Britain shipped, by weight, more tea to her troops than anything save bullets. Small arms ammunition, that is: the British army got through more tea than artillery shells. By weight. Contemporary soldier Spike Milligan observed that they were damn lucky that Rommel never tried baiting minefields with tea.
Arthur C. Clarke recounted in his autobiography that during WWII, one of his jobs in the civil service was to coordinate the dispersal of tea stockpiles throughout the country, as the government feared civil disorder if the main warehouses were taken out by a chance bombing.
In 1942 the Luftwaffe decided that, deprived of tea, the British Empire would pretty much grind to a halt. They therefore decided to bomb Mincing Lane - center of all British and Imperial tea trading - flat. It worked too. The tea industry was sent into chaos and on account of the confusion, tea was rationed to two ounces a week - which is very very little.note From a morale point of view it was one of the most successful bombing strategies of the war.
In response to shortage fears, in 1942 the British decided to buy the tea. As in all of it. In the world. That's right: in 1942, to fuel her soldiers, sailors, and airmen, Britannia bought the entire world crop of tea (except for the part of it under Japanese control, of coursenote ) - and it was as vital to her armies as bullets and tanks.
On D-Day, the British troops started to make tea on Sword Beach almost as soon as they landed, even though they were still under fire. Later, after the beaches were taken and troops started to move inland, the Americans got upset over reports that the British stopped advancing to make tea, as the plan called for soldiers to advance until nightfall in order to capture as much ground before the expected German counter attack.
These reports weren't strictly accurate; a few companies of infantry were ordered to hold position for a short period because they were getting too far ahead of their tank support. Brewing tea happened because it's standard practice in the British Army to grab any opportunity for a hot drink and preferably some food; it's good for morale, helps stave off the effects of British weather, and you never know how long it'll be before the next chance comes up.
Spike Milligan's mate Harry Edgington showed bravery under fire in North Africa. A German aircraft strafed their artillery position while Edgington was making a brew. Rather than duck for cover, Edgington took off his steel helmet and used it to protect the precious brewing tea, lest it get shot up...
One of the small, metal blast shelters on Normandy's Pointe du Hoc has the back completely blown out. While it may be an urban legend, the explanation some tour guides give holds that, after the area was captured, two British soldiers decided to make tea. For some reason, whatever they lit to heat the water caused a massive explosion. Their bodies were never recovered, and they were listed as missing in action.
During the German occupation of the Netherlands, the British dropped tea bags over Amsterdam. That's right, we gave them TEA TO FIGHT THE NAZIS.