The family of three-year-old Alfie Lamb said “justice has prevailed” after an ex-minister’s son was jailed for crushing him to death with a car seat.

Stephen Waterson, 26, reversed the seat of his Audi convertible, squashing his girlfriend’s young son in the footwell on February 1 last year.

He then orchestrated a “campaign of lies”, even threatening to make witnesses “disappear” to avoid responsibility for Alfie’s death.

The toddler’s aunt, Ashleigh Jeffery, eventually broke the wall of silence and recorded Alfie’s mother revealing what really happened.

A jury had failed to reach a verdict in Waterson’s trial and he pleaded guilty of manslaughter by gross negligence in September ahead of his retrial.

On Thursday, Mr Justice Kerr sentenced Waterson to seven-and-a-half years for manslaughter, plotting to pervert the course of justice and intimidating witness Marcus Lamb.

The judge said: “I do not find you were annoyed with Alfie and moved your seat back because of that annoyance.”

“Nevertheless, I am satisfied so that I am sure on the evidence I heard at the trial that albeit not in anger but for your own comfort, you moved the car seat back twice and not only once.”

Alfie Lamb manslaughter court case
Stephen Waterson crushed three-year-old Alfie Lamb to death with his car seat (Metropolitan Police/PA)

He accepted character references from the defendant’s father, the former minister Nigel Waterson and his wife Barbara, who attended court, and agreed he was “not all bad”.

But he said Waterson had been “cunning, manipulative, dishonest, disloyal, deceitful, threatening, controlling and sometimes violent”.

Earlier this year, Alfie’s mother, Adrian Hoare, 24, from Gravesend in Kent, was jailed for two years and nine months for child cruelty and her part in the conspiracy.

Pregnant barmaid Emilie Williams, 20, had admitted lying to police and was sentenced to five months’ imprisonment, suspended for 18 months, and 100 hours of unpaid work.

On the cover-up, Mr Justice Kerr told Waterson: “You orchestrated the campaign of lies, assisted by Ms Hoare who had the misfortune to fall in love with you and was willing to lie to protect you and herself.

“When the conspiracy began to falter in the second half of February 2018 under pressure from a very brave young woman, Ms Ashleigh Jeffery, you resorted to threats of violence, saying you could make people disappear.”

Alfie Lamb manslaughter court case
Alfie’s mother Adrian Hoare was ‘unlucky enough to fall in love’ with Waterson and was caught up in the lies. (Met Police/PA)

Speaking outside court, Ms Jeffery told how the family had been “utterly devastated” by the death of “a very happy three-year-old boy with his whole life ahead of him”.

She said: “The tragic circumstances surrounding his death is something we will never come to terms with.

“No sentence will ever be enough, but today we finally gave Alfie a voice and justice has prevailed.”

In a victim impact statement, she also said Waterson’s guilty plea had been “like a huge weight had been lifted”.

Ms Jeffery, who had given key evidence in court, said: “He could have avoided so much more upset in people’s lives had he just owned up in the beginning.”

Detective Chief Inspector Simon Harding described Waterson as a “very arrogant, selfish, controlling and manipulative man”.

He said: “He knew what happened. He tried to put my officers off the scent from the word go.”

He paid tribute to Ms Jeffery, saying she had been “incredibly strong and brave” in her determination to find out what happened and “changed the course of the investigation”.

It is the first time anyone in the UK has died from crush asphyxiation as a result of an electronic car seat, police said.

Alfie Lamb manslaughter court case
Stephen Waterson and Adrian Hoare with Alfie Lamb were caught on CCTV during a shopping trip to Sutton on the day he died (Metropolitan Police/PA)

Waterson and Hoare had gone shopping for cushions in Sutton, south London, accompanied by Alfie, Williams, Marcus Lamb, 22, and another young child.

Nightclub worker Waterson wanted to stretch his legs out and twice moved his front passenger seat into Alfie as he sat at his mother’s feet, jurors heard.

By the time they arrived at Waterson’s home in Croydon, the little boy had collapsed and he died from crush asphyxia three days later.

Alfie Lamb manslaughter court case
Nigel Waterson and Barbara Judge, parents of adopted Stephen Waterson, remained tight-lipped after their son Stephen was sentenced at the Old Bailey (Kirsty O’Connor/PA)

In mitigation for Waterson, Tana Adkin QC told the court: “Whilst thoughtless, I have no doubt, and selfish in his behaviour on February 1, he was not deliberately malevolent and nasty towards Alfie.”

Waterson’s father Nigel Waterson was first elected MP for Eastbourne in 1992 and was a junior minister in John Major’s government, but was defeated by Liberal Democrat Stephen Lloyd at the 2010 general election.