Mix milton with washingup liquid about 2/3 milton to 1/3 liquid and scrub it on with an old toothbrush then leave it for a hour or so, maybe even overnight. The washing up liquid breaks down the water tension bond of the milton and lets it seep into the tiny pits and scratches that are holding the tea stain
That's a great tip, Woof. Have also heard that using Steradent tablets made up as a paste or strong solution can be good for stains like tea and coffee.
I have (25 year old) pale grey worktops which get badly stained with tea, I use Hob Brite (for sinks) available from supermarkets, it's better than bleach. It is supposed to be for cooker hobs but I use it for cleaning the sink and the white teapot comes up a treat! On Amazon but check supermarket prices first ........
Amazon.co.uk User Recommendation
Toothpaste usually works well on this sort of thing, Scrubbed in with an old toothbrush, or soluble aspirin made into a paste, scrubbed in with toothbrush again.