Major delays hit the Jubilee line on Friday morning after reports of a man with a knife at Canary Wharf.
Police searched a train at the station but could not find the offender.
The alarm was raised at around 9am and caused major problems between London Bridge and Stratford.
The offender was reported to have originally been seen on the Central line.
A British Transport Police spokesman said: "Officers were alerted to reports of a man carrying a knife on board a Central line train service on Friday, 6 March, shortly before 9am.
"The man is thought to have travelled on a Jubilee line service to Canary Wharf. Officers searched a train at Canary Wharf, but no one was found matching the description."
A spokesman for Transport for London tweeted: "No service between Stratford and London Bridge and minor delays on the rest of the line while the police carry out an investigation."