London coffee

I just want to confirm that one can get excellent, non-chain, and above all non-hipster-bitterness-sour coffee in London with enormous ease, these days.  On the top, in a beautiful old dairy on Warren Street (which my father reminds me used to be a very unsalubrious "and popular" street indeed); at the bottom, by Great Portland Street station (I preferred the dairy, but the Black Sheep helped caffeinate me further before a long day attending a meeting that happily was a master-class in chairing a complex agenda with exemplary tact and efficiency).  Oh, and yes, my father does remember enjoying dining at the top of the Post Office Tower, although says the food was utterly unmemorable ...