A railway staff member who "saved many people's lives" is in a life-threatening condition after he was injured trying to protect train passengers from a knifeman.

The intervention by the London North Eastern Railway (LNER) worker, who has not been named, was described as "heroic" by a police spokesman.

A 32-year-old man is the only suspect after the attack on a train from Doncaster to London King's Cross, which stopped in Huntingdon, Cambridgeshire, shortly before 20:00 GMT on Saturday.

Eleven people were treated in hospital after the attack. On Sunday evening, British Transport Police (BTP) confirmed five casualties had been discharged.

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."

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.