The parents of a two-week-old boy found in his cot at a special care baby unit with “catastrophic injuries” walked out to have a cigarette as medics attempted to resuscitate him, a court has heard.

Brendon Staddon had suffered a shattered skull and broken neck, his injuries so severe they were compared to those of someone who had fallen from a high building, a jury at Bristol crown court was told.

Brendon’s parents, Daniel Gunter, 27, and Sophie Staddon, 21, deny murder and also plead not guilty to causing or allowing the death of a child.

Jurors heard that Gunter was allegedly controlling and sometimes violent to Staddon and had expressed doubt that the child was his.

Charles Row KC, prosecuting, said Brendon was born at 33 weeks in February last year at Yeovil district hospital, weighing less than “a couple of bags of sugar”.

He seemed to be doing well but just after 4am on 5 March, Staddon approached the nursing station and asked the staff to check her baby.

Row said: “Staff found him lying in his cot with his baby grow open. He had suffered catastrophic injuries.”

The barrister described the attack as exhibiting “sheer brutality” with “hardly a part of his body spared”.

He said: “In plain language, his head had been crushed so as to shatter his skull. He was badly bruised from head to toe, with deep scratches to his neck. He was found to have, amongst other injuries, a broken neck, a broken jaw, broken legs, broken ankles and broken wrists.”

The prosecutor said one medical expert likened the injuries to those that might be found in a fall from a multi-storey building or in a “complex” road accident.

Row said on occasion Gunter would be violent towards Staddon. She allegedly said he would shout in her face, had hurled cups and plates at her and had thrown her across a room.

He allegedly controlled her finances, dictated who she could speak to and spend time with, what and how much she ate and when she smoked. She told one acquaintance Gunter had said he did not want the baby, the court heard.

Row said the authorities were worried about the couple and meetings had been held to decided if Brendon should be taken into care when he was born.

Staddon and Gunter looked after the child in hospital but nurses were concerned about how he handled the child. On the day before he died, Staddon was upset because Gunter had allegedly said he wasn’t the father. Such was the concern from staff that security were alerted.

At about 3.30am on 5 March a nurse looked in on the parents and Brendon and asked if the child was alright. Row said: “His [Gunter’s] reply did not seem natural. He seemed excited, his response was unusually animated.” The nurse could not see anything of Brendon as he was swaddled in a blanket.

Just after 4am Staddon approached the nursing station and asked that Brendon be checked as he was cold. A nurse examined him and raised the alarm.

Gunter and Staddon left at 4.40am to go outside for a cigarette. “They did not return, nor did they seek any update on their child’s condition,” Row said.

When they were arrested, Gunter told police: “She’s my witness and I’m her witness.” As he was being led to a van, the court heard that Gunter said to Staddon: “Promise me, stick together yeah.”

The trial continues.