A “surge” in police presence at major rail terminals – including London, Birmingham, Leeds, York and Manchester – is expected until at least Tuesday.
A 35-year-old man, who was also arrested at the scene, has been released with no further action after it was reported “in good faith” that he had been involved in the attack. Officers later confirmed this was not the case.
The force confirmed the LNER staff member in life-threatening condition had tried to stop the attacker.
“Having viewed the CCTV from the train, the actions of the member of rail staff were nothing short of heroic and undoubtedly saved people’s lives,” a BTP spokesman said.
The suspect, a black British man from Peterborough, boarded the London North Eastern Railway (LNER) train at the city’s station, the force said.
Dep Chf Con Stuart Cundy added: “Our investigation is moving at pace and we are confident we are not looking for anyone else in connection to the incident.”
“As would be expected, specialist detectives are looking into the background of the suspect we have in custody and the events that led up to the attack,” Cundy added.
The force said a knife had been recovered by officers at the scene.
The motive of the suspected attacker is still unknown, though police have said that they do not believe the incident was motivated by terrorism.
