My point exactly: Because there are so many accents in the UK, in order to understand most people you happen to meet in one day (in the tube, having a pint at the pub, shopping, talking to the server at the restaurant, etc.), it's OK if your ESL teacher had a strong accent (Russian or other) because at least you will understand that type of accent.

I vividly remember the first time I went to London: the nice receptionist (at an OK hotel) told me something like aiiielloooo. I made her repeat twice. It was embarrassing for both of us because it was the very first word that she told me. She was simply trying to say Hello. My tolerance to various accents was more important in that setting than having studied with a native English teacher. It's in the mind. Not in the way you position your tongue behind or between your teeth.