Tea would be an unusual drink to ask for in a restaurant (as opposed to a cafe) unless they do breakfast/brunch, or you were partaking of “afternoon tea” (a rare treat for the ordinarily incomed).

If it was “afternoon tea” you would be offered a menu of different teas to choose from and it would be served with a tiered tray of finger sandwiches and pastries. And you would be charged a ridiculous amount of money for what is basically a small picnic.

If you were ordering tea as a drink in a restaurant, it would most likely come in a small teapot (with a teabag unless it was a very posh place), possibly some extra boiling water to refresh the pot after you’ve poured some tea, a cup and saucer, a small jug of milk, and a bowl of white sugar or sugar cubes (or a selection of packets of sugar or sweetener if it was not such a posh place).

If you asked for tea in a cafe, depending on how fancy the cafe is, it might look similar to the restaurant offering, or it might be a teabag in a mug of boiling water, pots of UHT milk, and packets of sugar.

No one would ever assume you wanted iced tea unless you specified it. And if you did specify it, they would most likely look blank and say they couldn’t do it. I can’t recall ever seeing it on a menu. Hot tea would be providable by any establishment whether or not it was on the menu because pretty much every kitchen in the UK has teabags in it.