London Overground trains are unable to run between Surrey Quays and Clapham Junction due to a points failure at Denmark Hill, causing major disruption for commuters this afternoon.
The issue also sparked chaos on Southeastern between London Victoria and Gillingham and Thameslink between London Blackfriars and Sevenoaks.
Transport chiefs warn the delays of up to 20 minutes or cancellations are expected to continue until the end of the day.
It comes after the Circle, Metropolitan and Hammersmith & City Lines were hit by delays due to a faulty train at King’s Cross St. Pancras.
On the roads, the M25 clockwise (northbound) entry slip at J11 has reopened following an earlier vehicle fire.