Some London borough boundaries are easy to cross. The boundary between Croydon and Bromley, for example, is 10 miles long and can be crossed in over 40 different places.
But other London boundaries are much harder to cross, or in a few cases impossible except by boat. So let's investigate...
The London borough boundaries with fewest crossings
It's best to do this in two parts.
a) Boundaries along the River Thames
Starting out east...
Havering → Bexley: 0 (big estuary, no crossing points)
Barking & Dagenham → Bexley: 0 (ditto)
Barking & Dagenham → Greenwich: 0 (technically 1 if you catch a Thames Clipper from Barking Riverside to Greenwich, but physically zero)
Newham → Greenwich: 7 (three railways, one road tunnel, one foot tunnel, one Dangleway and arguably the Woolwich Ferry)
Tower Hamlets → Greenwich: 5 (two railways, two bores of the Blackwall Tunnel, one foot tunnel)
Tower Hamlets → Lewisham: 0 (boundary is less than 1km long, so zilch)
Tower Hamlets → Southwark: 4 (one bridge, one tunnel, two railways)
City of London → Southwark: 8 (three bridges, one footbridge, two railway bridges, two railways)
City of London → Lambeth: 0 (boundary is less than 200m long, so zilch)
Westminster → Lambeth: 11 (four bridges, two footbridges, one railway bridge, four railways)
Westminster → Wandsworth: 2 (one bridge, one railway bridge)
Kensington & Chelsea → Wandsworth: 3 (three bridges)
Hammersmith & Fulham → Wandsworth: 4 (two bridges, two railway bridges)
Hammersmith & Fulham → Richmond: 1 (one bridge, closed to traffic since 2019)
Hounslow → Richmond: loads (because the boundary veers inland above Isleworth)
Westminster to Lambeth is the easiest borough boundary to cross, as you might expect given how central it is.
The five uncrossable boundaries are Havering → Bexley, Barking & Dagenham → Bexley, Barking & Dagenham → Greenwich, Tower Hamlets → Lewisham and City of London → Lambeth. The new Thamesmead DLR extension won't change this. The Thames is currently uncrossable for over 10 miles downstream of Woolwich. The really bad severance out west is between Hammersmith & Fulham and Richmond, a two mile boundary where the only Thames crossing is Hammersmith Bridge which may never carry vehicles again. The actual severance for road traffic is 4 miles.
b) Boundaries away from the River Thames
Now it gets interesting...
i) Lambeth → Bromley: 1
The hardest-to-cross borough boundary is between Lambeth and Bromley. There is only one place to cross and this is it.
This is the Vicar's Oak road junction at Crystal Palace. It's famous as the only place in London where four boroughs meet, or at least they used to but Southwark has since been nudged slightly north. This leaves 75m where Lambeth marginally meets Bromley and the boundary runs down the middle of Crystal Palace Parade.
Technically you can cross this brief stretch of road anywhere but it's dangerous and the only safe place is this pedestrian crossing. The crossing is via two traffic islands and the actual dividing line is on the first if coming from Lambeth (closest to the Westow House pub). This is close to where the Vicar's Oak once stood, long before this was a signalised road junction.
Road traffic driving from Anerley Hill into Crystal Palace Parade also passes from Bromley into Lambeth, as do buses turning right out of the bus station. Traffic driving south down Crystal Palace Parade does not enter Lambeth. But for pedestrians there's just this one crossing, the fewest connections across any borough boundary away from the Thames.
ii) Redbridge → Havering: 2
Unless trespassing, there are only two ways to cross the Redbridge/Havering border. One is the B147 at Collier Row, otherwise known as Hog Hill Road. The other is a footpath across Hainault Golf Club, which you may have walked because it's part of London Loop section 20. Just two connections in two miles... that's private land for you.
iii) Kingston → Sutton: 3
On the opposite side of London is a paltry set of connections in the Worcester Park area. One is the main road under the railway bridge by the station, this the route taken by all the buses hereabouts. The other two are at opposite ends of Caverleigh Way where a small estate of five streets in Kingston can only be accessed via Sutton. The railway line does not switch boroughs. iii) Kingston → Wandsworth: 3
Kingston has another three-crossing boundary near the Robin Hood Roundabout on the southern edge of Richmond Park. One is a main road, the A3, where it changes from Kingston Vale to Roehampton Vale. The others are two footbridges over the Beverley Brook. They connect two sets of playing fields adjacent to Wimbledon Common, and Capital Ring section 6 crosses one of them.
iv) Brent → Kensington & Chelsea: 3-ish
Nominally there are only three connections between these boroughs - the two gates into Kensal Green Cemetery and the brief cul-de-sac of Alma Place. However the ½-mile-long boundary actually runs down the centre of Harrow Road, not along the wall of the cemetery, so is easily crossed in many places.
v) Enfield → Waltham Forest: 5
Two main roads (including the North Circular), two minor roads and a glum reservoir-adjacent footpath. v) Haringey → Waltham Forest: 5
One road (Ferry Lane at Tottenham Hale), two railways and two footbridges at Tottenham Marshes.
vi) Southwark → Bromley: 5
And finally back to Crystal Palace and the continuation of Crystal Palace Parade along the western edge of Crystal Palace Park. Again the precise boundary passes down the centre of the road and there are just four pedestrian crossings along this half mile stretch. The railway tunnel west of Crystal Palace station knocks the number of connections up to five.
The other 59 London borough boundaries have more crossings, unless you know better.
