Se1 is a big area but I would suggest that you pop-into the "Gladdy" as it's known by many and see what you think. It can be very cliquey at times, but it is usually friendly. Watch out for Camilla aged 88 who has drank there for nearly 40 years! You won't be able to miss her either at the bar sipping whisky or creaming the jackpot off the fruit machine.
I typed \\\'bars\\\' into scoot, and it gave me the option to choose gay bars .. I was surprised to the extent of the list. However I am aware of the Jubilee Tavern by Waterloo station, and the Fort on Grange Road if you really like to slum it. It is a shame that The Bridge, near London Bridge closed, as the roast and bottle of wine for 2 on Sundays was a real favourite of mine!!
Just saying we had a really good New Years Eve there the other night. Really glad Sean and Paul returned to run it in the autumn after a few months away over the summer - its back to its old self: a well run, friendly local pub, with reasonable prices.