It is (or was) considered "lower-class" to drop your Ts in the UK. But these days, it's not fashionable to talk like Boris Johnson, even if you went to Eton, so many upper-middle class people emulate aspects of "lower-class" speech, including the glottalization of "t" when it's followed by an unstressed syllable (like water). Even someone as indisputably posh as Prince Harry will T-glottalize on occasion.