The driver of a school bus that crashed on a Merseyside motorway last year died of natural causes, a coroner’s office has said.

Stephen Shrimpton, 40, died when the coach he was driving crashed on the northbound M53 in Wirral on 29 September. One of the passengers, Jessica Baker, 15, was killed in the crash.

A spokesperson for Liverpool coroner’s office said on Friday that Shrimpton’s case had been closed because the cause of his death had been found to be natural. No further details were released.

Baker was among about 50 students being taken to West Kirby and Calday Grange grammar schools.

Four other children were taken to hospital, including a 14-year-old boy whose injuries were said to be life-changing, Merseyside police said at the time. Others were handled at an emergency training centre, with 13 treated for minor injuries before they were released.

When the inquest into Shrimpton’s death was opened last October, the senior coroner for Liverpool and Wirral, André Rebello, said CCTV footage showed him slump to his left while driving the coach, which at the same time left the carriageway and went up an embankment before ending up on its side.

Rebello said it was miraculous that others had not been killed. He also noted that anyone over 14 was responsible themselves for wearing a seatbelt, but that clarity was needed over the rules on coaches and buses.

At the time, the coroner said further medical examinations would be needed to establish Shrimpton’s cause of death, with focus on the examination of the condition of his heart.

In a statement released after the crash, the driver’s family said: “Stephen was a loving husband and father to his wife and his wonderful children, a caring and thoughtful man who would always prioritise others over himself.”

An inquest for Jessica would be held at a later date, with a review hearing scheduled for July, the coroner’s office spokesperson said.

The inquest opening heard that the teenager, from Chester, was partially ejected from the vehicle and suffered instantaneous fatal head injuries.

Jessica’s family paid tribute to the talented climber, whom they described as a “warm-hearted, wonderful daughter, granddaughter and niece, devoted sister and loyal friend”.

More than £6,500 was raised through an online fundraising site for Climbers Against Cancer in her memory.