Drivers heading towards London from Kent are facing delays this afternoon after a crash partially blocked the M20 London-bound exit slip road at the Swanley Interchange, where the M20 meets the M25.
The incident was first reported at around 1.17pm on Tuesday (September 29), with lane one of the two lanes on the exit slip road affected. Traffic on the approach to the junction was slowing as motorists were forced to merge into a single lane, and delays of around 15 minutes were being reported for London-bound drivers.
Where exactly is the disruption?
The blockage is on the London-bound exit slip road of the M20 at the Swanley Interchange — the junction in north-west Kent where the M20 feeds directly into the M25, London’s orbital motorway.
It is one of the key gateways for traffic travelling from Kent, the Channel ports and the wider South East towards the capital, meaning even a partial blockage during the busy afternoon period can quickly cause tailbacks to build on the main carriageway.
M25 anticlockwise slip road closed
There is a further complication for drivers using the interchange. The slip road from the M20 onto the M25 anticlockwise remains closed following the crash.
Motorists can still get onto the M25 by using the roundabout at the Swanley Interchange, but the diversion is adding to journey times and putting extra pressure on the roundabout itself. The latest updates, posted shortly after 1.18pm, confirmed the closure was still in place, with drivers urged to allow extra time for their journeys.
What drivers should do
If you are planning to use the M20 towards London this afternoon, it is worth checking live traffic information before you set off. Live traffic cameras and journey planners can give you a picture of conditions at the Swanley Interchange before you leave the house or office.
Those already on the road should stay alert on the approach to the junction, keep a safe distance from the vehicle in front and merge in good time rather than leaving it to the last moment. Sudden lane changes at busy interchanges are one of the most common causes of secondary collisions, and nobody wants a second incident on top of the first.
Drivers heading for the M25 anticlockwise who would normally use the direct slip road should follow the signed diversion via the interchange roundabout. Depending on where your journey starts, it may also be worth considering alternative routes into London, such as the M2 and A2 corridor, although these are likely to be busier than usual as drivers seek to avoid the disruption.
Why the M20–M25 interchange is a notorious pinch point
The Swanley Interchange — where the M20 meets the M25 — is one of the busiest motorway junctions in the South East, and it does not take much to throw it out of balance.
The M20 is the main artery for freight travelling between London and the Channel ports at Dover and Folkestone, while also carrying heavy commuter traffic from towns across Kent into the capital. All of that traffic converges at Swanley with vehicles already circulating on the M25, one of the busiest motorways in Europe.
That is why a single-lane blockage on an exit slip road can so quickly translate into 15-minute delays. With nowhere for traffic to go except through the interchange roundabout, any restriction at the slip roads immediately ripples back onto the main carriageway — and, at peak times, for miles beyond it.
Wider disruption on London’s roads today
The M20 incident comes on a difficult day for drivers across London and the South East. All M25 lanes were halted near Iver Heath earlier today after a separate crash, triggering long queues on the orbital motorway.
Elsewhere, a four-vehicle crash caused traffic chaos on the North Circular, while a crash shut The Ridgeway in Mill Hill as emergency services dealt with the incident.
With several incidents affecting key routes at the same time, drivers are advised to check their full route before travelling and to build in plenty of extra time.
This is a developing story — check back for updates.
