AIUI (or rather, as my dentists have told me down the years), tea and coffee (and I think red wine and a few other things - Corsodyl is particularly bad) do stain your teeth - you can get them cleaned (typically by the hygienist on a private basis rather than by the NHS dentist) with an ultrasonic device. But I think once stained, they won't really become un-stained without cleaning.

A previous dentist did the cleaning for me, the current one doesn't (but does ask me if I want to see the hygienist every time I go), and I can't be bothered since it's only a cosmetic defect and doesn't affect the durability of the teeth.