How many consecutive London bus routes can you ride?
For example, if you could ride the 3, then the 4, then the 5, then the 6, that'd be four consecutive bus routes. But you can't, because route 3 and route 4 never quite meet, and route 5 gets no closer to central London than Canning Town station. So not that.
For the avoidance of doubt, I'm allowing interchange if two routes cross or overlap - they don't have to share the same bus stop. No long walks are allowed. Oh, and numbered buses only, no letters. If I'd allowed letters then the best run would be in Orpington where all eleven 'R' buses (from R1 to R11) stop in the High Street. So not that.
With over 400 numbered London bus routes, you'd think there'd be a decently long chain of consecutive bus routes somewhere. But I couldn't find one. London's bus routes aren't laid out sequentially in convenient geographical sectors (or if they ever were, enough tweaks have been made since to wreck the pattern).
For example, out in Dagenham the 173, 174 and 175 all run down the Heathway, which looks promising. But the 172 goes to Brockley and the 176 goes to Penge, so that doesn't help. Meanwhile at Elephant & Castle the 343 links to the 344, which links to the 345 in Battersea, which looks promising. But the 346 only serves Upminster, and the 342 doesn't exist, so that's no help either.
The longest chain I've managed to find is just five buses long, and starts with the 22.
22 → Oxford Circus station 23 Oxford Circus station → Trafalgar Square 24 Trafalgar Square → Tottenham Court Road station 25 Tottenham Court Road station → Bank station 26 Bank station →
There are some very familiar changeover points there. Oxford Circus, specifically the top of Regent Street, is the only place where the two buses serve the same stop - at the other interchanges you have to take a short walk. Obviously I'm not suggesting you do this for real, it's just a thought experiment. But if you did ride these five consecutive buses it'd take about an hour, just saying.
I don't think there's a chain of 6 routes. I don't think there's another chain of 5. Unless you know better.
If you're planning to check for the longest chain, obviously what you need is a bus map. Unfortunately TfL stopped producing London bus maps in March 2016, and took them off their website last year. This saves them money, but leaves us in the dark, because why should passengers know where all the buses go? If you'd like a digital copy of the final TfL bus maps, they're all here as pdfs: [Central][NW][NE][SW][SE]. Even better, if you'd like digital copies of all the final TfL bus maps as printed, including covers and indexes and all the inserts, they're in these zip files. Alas the maps are already long out of date, especially in central London. But hurrah for Freedom of Information requests (and boo to busmapkillers).
Here's an intriguing thing.
Ten years ago, the longest chain I can find was 6 buses. 11 12 13 14 15 16
Forty years ago, it was seven. 10 11 12 13 14 15 16
Seventy years ago it was ten. 10 11 12 13 14 15 16 17 18 19
The further back you go, the longer the chains get because bus routes were longer and better connected. Inexorably over time they've got shorter, or been changed, and so become harder to connect. For example, the 11 no longer quite meets the 10 (which is about to be scrapped), the 13 was sneakily renumbered (so no longer overlaps the 12) and the 15 no longer passes through Piccadilly Circus (so now just misses the 14).
As we enter the Hopper Era, expect bus routes to get shorter still. Indeed my 22 → 26 journey is about to be wrecked in 10 days time when route 23 is diverted away from central London and merged with route 10. Moreover, route 25 is about to be cut back from Oxford Circus to Holborn Circus, maybe imminently, breaking the link with the 24.
In the near future, the longest chain of consecutive bus routes is going to be only 4 buses long, down from 5, down from 7, down from 10. That's our direction of travel. I mean, I assume there must be a chain of 4 consecutive bus routes somewhere in London. Help me out, I'm still looking...