It's possible to visit four London boroughs on foot in 1 minute 10 seconds.
Bromley → Croydon → Lambeth → Southwark (report from Crystal Palace here)
It's possible to visit five London boroughs on foot in less than 10 minutes.
Bromley → Croydon → Lambeth → Southwark → Lewisham (same report here)
For my latest challenge I've tried walking the maximum possible in an hour, which turns out to be eight.
Tower Hamlets → Hackney → City of London → Islington → Camden → Westminster → Southwark → Lambeth
This can only be done in the centre of town where administrative boundaries lie very close together, so what follows is essentially a walk around the City of London and the seven immediately adjacent boroughs.
I started at Norton Folgate, just north of Spitalfields Market and Liverpool Street station. This is one of the former liberties of the City, most recently desecrated by British Land as the site of a dense office pile, and also the point where Tower Hamlets, Hackney and the City of London meet. That was three boroughs ticked off instantaneously, or would have been had I been able to stand safely in the very centre of the road at the junction with Worship Street.
By my calculations there are 50 points in Greater London where three boroughs meet, not that you can physically stand at all of them without trespassing or drowning, but ticking off three boroughs very very quickly is not a tough challenge.
Follow Worship Street west and four minutes later you magically enter Islington... or at least on any normal day you do. Alas when I turned up yesterday the last section of the road was blocked for filming, with a heck of a lot of vans and lights and cameras stashed in readiness and a security guard intent on keeping pedestrians out of shot. I have no idea what they were filming, only that it required a lot more vehicles than you normally see, and it wasn't a problem because I simply walked one block south and entered Islington via Christopher Street instead. 4 boroughs - four minutes
That was the low-hanging fruit taken. The next nearest unvisited borough was Camden on the other side of the City so what came next was a walk of just over a mile to get there. In good news that walk was mostly along the B100, a road I blogged in its entirety earlier this month so don't need to describe again. Think Chiswell Street, the Beech Street tunnel and Smithfield market, eventually ending up on Farringdon Street.
I could have reached Camden quicker but instead I targeted the triple point where Camden, Westminster and the City meet. This is roughly in the middle of Chancery Lane (between King's College and the Law Society) and deftly raised my borough total to six. What's more I'd walked it in half an hour flat, which I think is the quickest it's possible to hit half a dozen. 6 boroughs - thirty minutes
Two other London boroughs were now less than half a mile away but on the other side of the Thames. Had the Garden Bridge ever been built it would have been easier to get there via a more direct route, but thankfully it wasn't. Instead my choice was whether to head upstream to Waterloo Bridge or downstream to Blackfriars Bridge, and crossing the latter turned out to be quicker.
Blackfriars Bridge is one of two that lie entirely within the City of London so I didn't enter Southwark halfway across, I had to wait until I got to the other side. 7 boroughs - forty-four minutes
Finally it was a short walk west along the South Bank below Sea Containers House. This was by far the most congested part of the route, especially the narrow stretch beside the Oxo Tower where some careful sidestepping was required. But immediately beyond this I crossed into Bernie Spain Gardens and entered my eighth borough, which was Lambeth, so I could stop the clock. 8 boroughs - forty-eight minutes
A slightly more streamlined route at a slightly faster pace might have allowed me to hit 45 minutes, but eight different boroughs in under an hour cannot be beaten.
Because I'd been walking around the innermost part of the city it would then have been a bit of a hike to reach a ninth. The nearest was Wandsworth at Nine Elms and that's a couple of miles distant (so, notionally, walking nine boroughs would take an hour and a half).
As for Kensington & Chelsea that would have required getting to the north side of Chelsea Bridge (meaning ten boroughs is just doable in two hours). Hammersmith & Fulham would have added another half hour, and had I felt the need to add Richmond, Hounslow and Ealing at least one hour more. That would have been 14 boroughs in 3½ hours, but I had no interest in schlepping that far so stopped at eight.
Minimum time to walk to a number of London boroughs
It's important not to get too carried away with this. The question of how long it would take to walk to all 33 London boroughs sounds tempting to tackle, but because it would involve dropping in on Hillingdon, Havering and Crystal Palace is an entirely impractical activity. My walking challenge was essentially linear, but once you end up in two dimensions everything quickly gets much too complicated.
I have previously visited all 33 boroughs by train in 7 hours 13 minutes, because I do love ticking things off, and earlier this year made a special effort to walk through four English counties in one hour flat. I need to remember that you will never do this because you have either common sense or a life. But eight boroughs in quick succession is almost fun, should you ever have an hour to spare.