Armed police officers searched a London Underground train on Tuesday in search of someone they believed had attacked a man.
British Transport Police stormed a train on the southbound Victoria Line at Kings Cross, in search of a suspect who had left a 63-year-old man with cuts to his body and face.
People reported being held for up to 20 minutes on the train while it was searched.
BTP did not locate the suspect on the train. They later arrested a man at the Heathrow Terminals 1,2,3 tube station on suspicion of inflicting grievous bodily harm.
A BTP spokesman told HuffPost UK they were called to reports of an injured man at Finsbury Park station at 1.48pm on Tuesday.
They and the ambulance service arrived on the platform and the man was taken to hospital. His injuries are not thought to be life-threatening.
The armed officers then searched the train at Kings Cross, the next station but one.
The Victoria Line has "severe" delays during the incident but everything has now re-opened.