Nottinghamshire Police were called to a residential area in Balderton, near Newark-on-Trent, over concerns for a man's safety just before 7pm last Thursday.

Sergeant Graham Saville, a response officer based at Newark police station, suffered serious injuries after being struck by a train during the incident and was taken to Queen's Medical Centre in Nottingham.

The 46-year-old officer died in hospital on Tuesday with his family by his bedside, the force said.

Flags across the force will be flown at half-mast as a mark of respect.

The 29-year-old man he was assisting is believed to have non-life-threatening injuries.

Chief Constable Kate Meynell said in a statement: "Today is a day of mourning for the entire police family."

She described Mr Saville as a "hugely respected and popular colleague" whose death "has come as an enormous shock to us all".

'Devastating news'

Ms Meynell said it was "impossible to put into words how devastating this news is for everyone who loved and respected Graham".

"On Thursday, he went to work to protect the people of Nottinghamshire from harm, and it is testament to his bravery and dedication as a police officer that he was fatally injured while attempting to save another man's life."

She added: "His service and sacrifice will never be forgotten."

Nottinghamshire Police Federation branch chair Simon Riley said: "Graham was the epitome of what we should all strive to be as police officers."

The Prime Minister Rishi Sunak said: "I'm saddened to learn of the passing of Sergeant Saville.

"It is a testament to his bravery that he died in the line of duty and a terrible reminder of the work the police do every day to keep us safe.

"My thoughts are with his family, friends and the whole of Nottinghamshire."

Home Secretary Suella Braverman said: "I offer my deepest condolences to the family and Nottingham Police colleagues of Sergeant Graham Saville, who has lost his life after saving a man in distress on a railway line.

"We owe our police officers an immense debt of gratitude for their bravery while protecting us all."

Dan Fletcher, who has been referred to locally as a former police officer, set a crowdfunding effort for Mr Saville's family at the weekend with an initial target of £50,000 which has now been increased to £100,000.

An investigation into the incident, led by British Transport Police (BTP), is ongoing.

The man the officer was helping 'sustained electrocution injuries'

BTP said in a statement on Tuesday: "Enquiries confirmed that the officer was struck by a train whilst responding to an incident involving concern for the welfare of a man.

"The man, a 29-year-old, sustained electrocution injuries, and was also taken to hospital where he remains with injuries which are not believed to be life-changing."

Assistant Chief Constable Allan Gregory, of BTP, said: "It is one of the darkest days in policing to lose an officer in the line of duty, and Sergeant Saville's loved ones will be at the forefront of our minds throughout our enquiries."