Tragic Alfie Lamb was crushed by his mother’s boyfriend when he lashed out with his car seat “in a fit of childish temper”, jurors have been told.

Prosecutor Duncan Atkinson QC alleged the three-year-old suffered irreversible injuries when his mother’s boyfriend twice reversed his chair into him as he sat in a footwell of his Audi convertible.

But a defence lawyer for Stephen Waterson suggested Alfie could have died because his head was “pushed down as he cried himself to sleep” between his mother Adrian Hoare’s legs.

Waterson, 25, son of ex-minister Nigel Waterson, and hairdresser Hoare, 23, have both denied responsibility for Alfie’s death.

Alfie Lamb manslaughter court caseFormer Conservative minister Nigel Waterson and Barbara Judge arrive at the Old Bailey (Kirsty O’Connor/PA)

In his closing speech, Mr Atkinson said Waterson pushed his seat back because he wanted more leg room or he was annoyed at the crying child.

And Hoare “fundamentally and fatally” failed her son by doing nothing on the journey home to Croydon, south London, on February 1 last year, jurors heard.

Mr Atkinson said: “No one is going to suggest either of these defendants wanted Alfie to die. In text messages between them they just wanted their ‘little fatty’ back, they just wanted him home.

“The question for you is whether Alfie died because without any thought for the consequences, Stephen Waterson moved his chair back whether because he wanted more room or because Alfie was annoying him, putting Alfie at risk, lashing out at him with his car seat in a fit of childish temper.

“The further question is whether the person Alfie was most entitled in the whole world to rely on when that happened, and had a duty to protect him from such harm, failed him fundamentally and fatally.

“Failed him by putting him in such a dangerous place which is why children have car seats, which is why you would never think of putting a child in a footwell.”

He said neither of the defendants had explained the pathologist’s findings “because they cannot admit what Stephen Waterson did and Adrian Hoare failed to stop”.

The lawyer reminded jurors that the other occupants of the car, Emilie Williams and Marcus Lamb, had said Waterson moved his seat back into Alfie.

Waterson’s three previous convictions for battery indicated he would “lash out violently” when challenged, the court heard.

Mr Atkinson said Waterson orchestrated and developed a series of lies, all designed to protect himself and avoid blame.

“You may think there is clear evidence of him seeking to manipulate those who were in the car with him and others, including his adopted mother, getting them to lie or blaming them,” he said.

Alfie Lamb manslaughter court caseCourt sketch of Stephen Waterson and Adrian Hoare (Elizabeth Cook/PA)

Waterson lied in an initial 999 call, at the hospital and again as he was quizzed by police about an incident in Crystal Palace Park when he allegedly put his foot on Mr Lamb’s head, accusing him of being a “grass”, jurors heard.

The prosecutor said: “Mr Waterson has everything to hide and everything to play for in that interview.”

Tana Adkin, QC, for Waterson, told jurors her client was “very easy to dislike and easy to blame”.

She said: “This case is tragic and you may think it is obvious that Stephen Waterson has not helped himself by the lies he has told, by his behaviour, but it does not mean he is guilty.”

She said there were “very real question marks” over whether Waterson moved his chair back more than once.

Ms Adkin suggested that while the chair could have been part of a “domino effect”, another explanation for the fatal injuries involved Alfie’s head being “pushed down as he cried himself to sleep”.

Hoare, who is originally from north Kent, denies manslaughter, child cruelty and common assault on Emilie Williams, who was in the car.

Waterson has pleaded not guilty to manslaughter and intimidation of the driver Marcus Lamb. The couple and Williams have pleaded guilty to conspiring to pervert the course of justice by making false statements to police.