posh banger boys
May I recommend Borough Market? Yes I think I may. Head directly to the south bank of the river Thames, near the London Bridge end. Just before you hit the bridge, there it is under the shadow of the Southwark Cathedral (yes and that of the infamous Shard).
Walk aimlessly around the many corners of the market like everyone else and marvel at the amount of cheese and meat products available. Be charmed by the variety of hand made sweets and desserts on display. It's not all just about food though; there's art, there's craft, there's agriculture and what have you.
Inevitably, your legs will start to hurt, and your belly will growl. Of course you can be clever about all this and eat your way through the market for absolutely free by 'sampling' all the edible produce offered you, but seriously what you want to do is stumble upon the Posh Banger Boys. Contrary to the name, there's nothing at all posh about this burger (and sausage and etc) hut. There will probably be a queue, but it is worth waiting. The maestro will conjure you a mean burger. Be careful not to bite your fingers off while eating, but you're allowed to shake your head in wonder as you chew.
Vegetarians, vegans, health conscious types, e.t.c, do not despair. Borough Market is basically paradise for you too. There are dozens, scores even, of places to partake of the merriments. This market is a particular favourite of my homie the health food crazy chic from the Health Hacker Society blog.
Like many markets in London, it is steeped in centuries of history if you're interested. Or you could just enjoy the visual charm of the place and soak in the ambiance of old London.