Trains to Brighton and Hove are delayed this evening after police dealt with a disruptive passenger at East Croydon.
Reports from commuters stuck on trains suggest police believed a man had a gun on board a train from Caterham to Victoria.
Emergency services were called at about 6pm and a man was subsequently taken off the train.
Trains are now running, but Southern Rail says they are still delayed by up to 30 minutes.