Thanks for the expressions of interest. It would be a shame if there were no Brommies - the last time I did one of these it was won by three guys on unicycles, so there's a challenge for you!
I'm still in the planning phase but the broad plan is as follows:
Meet at HPC and, if you haven't already arranged it, hook up into teams of 2-4 (any more is unwieldy and a bit unfair). You'll each be given clue sheets and sent off at intervals of a couple of minutes. To avoid congestion at the clue locations, there will be variations on the order of the questions, so teams may not all head off in the same direction! Everybody will visit the same locations, eventually, though.
You'll need an A-Z or suitable mapping app, unless you have a cabbie's knowledge of central London, as for most of the clues, all you will be given by way of direction will be the name of street on which to look (NONE will be on busy streets, though, for safety reasons).
Whichever route you take, after a couple of hours you'll all come back to the same finish location, which will almost certainly be a pub, where I will wait to add up the scores. Fastest back will be declared the winner, but there will be time penalties for missed or incorrect answers. No prizes, but a definite warm fuzzy glow of satisfaction on offer.