This place. I've only been there twice, but I will definitely return. Spectacular beers from their own brewery, amazing food, wonderful traditional pub atmosphere...vastly better than the "chain" pubs in London. When I told the bartender I was a homebrewer, generous samples of EVERYTHING started appearing in front of me. Oddly enough, they had one of the greatest APAs I've ever had.
What a luck discovery, we only ducked in there to get out of the rain, but stayed a few hours and came back later for dinner.
The Greenwich Union
EDIT: I stopped by BevMo today, and found these! So while I can't go back to the Greenwich Union anytime soon, at least I can enjoy their beer!