I gathered up my courage and took the bus to TeamWork, a pro shop that I found in the TimeOut shopping guide. It's the only photography equipment supply shop that seems to have a reasonable selection of decent tripods and doesn't have a seizure-inducing web site. It's on a quiet side street, blissfully far from the frenetic nightmare that characterizes the electronics shops on Tottenham Court Road.
I crept in and glanced around at the crowded shelves, the piles of photo paper, the collection of guys hunched over computer screens and nearly turned around and left. Then the tall skinny one with the ponytail smiled at me and asked if I wanted anything. So I quietly stammered about the Manfrotto tripod (the 055ProB) I wanted to try out, and he bounced out from behind the counter and set it up. He answered all my questions kindly and reversed the center column when I asked if it were possible, to see how close to the ground it would go. He talked me into the pan-and-tilt head with the quick-release plate, which was a third of the price of the ball head I'd picked from the site.
On the way home, my Oyster card pre-pay ran out and I had to pay in cash for the ride. You're supposed to pay for a ticket at the bus stop if you don't have a travel card or enough credit on your Oyster. The Filipino bus driver issued me a ticket and a stern reprimand that nearly sent me into an inappropriate giggling fit because he sounded exactly like one of my uncles. I have to go back to the shop on Monday to get the tripod strap I wanted - the one that has a loop on the end to keep the legs from banging into you - but other than that, I'm very happy.