The "arrogant" son of former Government minister Nigel Waterson has been jailed for the manslaughter of his girlfriend's infant son.
Stephen Waterson, 26, repeatedly tried to absolve himself of blame after three-year-old Alfie Lamb was crushed to death by his car seat in the footwell of Waterson's Audi convertible on February 15 last year.
Waterson, described by police as being "arrogant, selfish and deeply unpleasant", subsequently sought to distance himself from the death and lying to police as the prospect of a conviction loomed.
He was jailed for seven years and six months at the Old Bailey on Thursday.
Alfie's mother, Adrian Hoare, 24, from Gravesend in Kent, has already been found guilty of child cruelty and jailed for two years and nine months at the Old Bailey.
Jurors were initially unable to reach a verdict on Waterson's culpability, but he subsequently changed his plea to guilty to manslaughter by gross negligence on the day of his retrial.
Both Waterson and Hoare had admitted conspiring to pervert the course of justice by lying to police.
Waterson was also convicted of intimidating a witness and Hoare of assaulting another witness.
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It is the first time anyone in the UK has died from crush asphyxiation as a result of an electronic car seat, police said.
The court heard the defendants had gone shopping for cushions in Sutton, accompanied by Alfie, Williams, Marcus Lamb, 22, and another young child.
Jurors in the earlier trial were shown CCTV of Alfie running to keep up with his mother moments before he was put in the car for the journey back to Croydon, south London.
The court had heard how nightclub worker Waterson became annoyed at Alfie's crying and moved his front passenger seat into him as he sat at his mother's feet. The maximum space in the foot well was 30cm, and, at the touch of a button, that could be reduced to just 9.5cm.
When Alfie continued to moan, Waterson reversed again saying: "I won't be told what to do by a three-year-old," Hoare told jurors.
By the time they arrived at Waterson's home in Croydon, the boy had collapsed and stopped breathing. As medics desperately tried to revive him, Waterson fled the scene and Hoare spun a web of lies to protect her boyfriend, claiming she had been in a taxi.
Alfie, nicknamed "Little Tarzan" by the defendants, died from crush asphyxia three days later.
As police closed in, Waterson gave officers a false name and false statement, and sold the Audi.
He threatened to make Hoare and the other witnesses "disappear" if they did not stick with their fake stories.
Hoare eventually broke her silence and told her half sister Ashleigh Jeffrey what happened in a taped conversation handed to police.
But Waterson blamed Mr Lamb, who he regarded as a step brother, for being a "grass" and put his foot on his head during a violent assault in Crystal Palace Park which was filmed on his mobile phone.
Jurors in the first trial were told Waterson was a controlling womaniser who also had a violent temper with three previous convictions for attacking an ex-girlfriend and his sister's husband.
Giving evidence earlier this year, he denied he would hurt a child and said he moved his seat back once by up to an inch.
Waterson's father 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.