A teenager accused of murdering his baby son has told a jury he had drunk lager, vodka and taken MDMA before the alleged attack and admitted he had been accused of being “heavy-handed” with the child in the past.

But the boy, who was 16 at the time of the child’s death, told Winchester crown court he had loved the child and had not done anything to harm him.

The father, now 17, has been accused of causing the infant to sustain fatal injuries including a skull fracture, broken leg and rib fractures. Jurors have heard that the seven-week-old baby was also bitten on the nose in the alleged attack at the mother’s flat in Southampton in the early hours of 11 February.

The baby’s mother, aged 18 at the time, is on trial for child cruelty for allegedly failing to protect her baby or seek help for him. Both parents, who cannot be named, deny the offences.

Giving evidence, the father said he and the mother had gone to a gathering at a neighbouring flat where he drank and took MDMA.

The defendant, who told the court he experienced memory problems, said he did not remember returning to his partner’s flat that night but did recall seeing her crying with the baby in her arms.

He said: “[She] was sat on the bed with [the baby] in her arms in a very bad state. She was crying, panicking, shaking. I walked in and she stood up and said he was white, he wasn’t breathing, she didn’t know what to do. I said: ‘Call an ambulance.’

“She got up and said he wasn’t breathing, he was grey and white. She passed him to me, he wasn’t moving, he was literally stone cold. I was hugging and squeezing him, I didn’t know what to do until the ambulance was on the phone and told me what to do.”

He said he performed CPR on the baby as instructed over the phone until paramedics arrived to take the child to hospital.

The defendant said he did not remember saying to a neighbour: “What have I done?” He said the mother, now 19, had told him the baby had fallen off the sofa on to the hard floor.

He denied intentionally causing the child harm and said he had never stopped loving him.

The defendant said he had been told he was “heavy-handed” with the baby when he first looked after him but said he had taken in the criticism and “realised what I was doing wasn’t appropriate”.

Describing the birth of his son, the defendant said: “I was in a bit of a state, I was happy, it was the best day of my life. He was the best thing that happened to me and always will be.”

He said he did not remember pushing the child’s mother to the ground in October 2017 while she was pregnant, causing a bruise to her face, and said he was “devastated” that he had hurt her.

The trial continues.