Someone said :
I find they have changed the formula for Barry tea as I get this bitter taste from it and it leaves really bad tea stains at the bottom of cup.
It might be a change in how you brew it too, or even something as simple as if you've recently got a new kettle or tea pot (that makes the tea brew at hotter temperature closer to boiling point).
Black tea that is brewed longer becomes bitter, darker, and of course stains easier.
but you're right I think Barry's has changed slightly, I noticed it's nicer to drink black, (without milk) then previously.
Maybe the taste-testers have started taste-testing it with low fat milk or less milk in general.