I've always known them as infusers. The old fashioned ones that looked like a baby crocodile, (at least that's how I used to think of it when I used to get it out of the draw and play with it when I was a kid,)and the new ones, a little ball on a chain, are also called infusers.
Couldn't agree more, Jan, about Lemon Balm. Along with Russian Vine and Red Valerian it's up there with the most pernicious garden invaders of all time.
Bramah used to do them, but I think it's closed now, isn't it?
I've had one from a poundstore before (not in SE1, unfortunately). I'd call them infusers, or "tea eggs" (which might just be my personal name for the ones like an egg on a chain, so possibly best ignore that.)
Mrs I bought one recently. I'll try to remember to ask where from.
(You could use a tea pot and strainer at a push, but I know it's not as convenient for a one-cup brew)
One thing you can do with all those unwanted 'herbs' is to get a container and submerse them in water. After they have started to ferment they make a very good liquid fertilizer. But, be warned. Store it away from the house because it does pong in hot weather.
Funny Chalkey, years ago when I was more active in the garden I used to dump rhubarb leaves in water and when gloopy use the water to spray on greenfly, don't drink it though unless you want to meet your maker a bit quicker than you want, apparently leaves contain oxalic (?) acid...
Ikea does both types- dangly and snappy.
I love nettle tea. I read somewhere you're supposed to harvest it at a particular time of year, or it can taste bitter. Also, there are two types and only one is good for tea. Partially helpful, sorry.