I've just spent a few days in London for a mate's fiftieth birthday.
I've got one word of advice for fellow Northern beer-hounds heading for the capital: Wetherspoon's.
The pub chain is your best bet for well-kept and conditioned cask beer at the reasonable prices those of us from north of the Trent are used to paying, especially if, like me, you had CAMRA vouchers to use up by the end of the month. Indeed, in the suburb of west London where I was stopping, it was the only pub selling cask beer.
I'm not sure I've drunk beer from Sambrook's Brewery in Battersea before, but the couple of pints of their Powerhouse Porter and (after that ran out) their Junction bitter were easily the best, and certainly cheapest, I found in the metropolis.
I also got to drink in the pub in Clerkenwell where Lenin drank when editing the Russian socialist newpaper Iskra nearby in 1903, and where he later allegedly first met Stalin. Although the building looks pretty much the same as it might have done then, the clientele has changed somewhat.