The widow of Pc Andrew Harper has said she is "disappointed" after the Court of Appeal rejected a bid by the Attorney General to increase the sentences of her husband's killers.
Henry Long, 19, was sentenced in July to 16 years and 18-year-olds Jessie Cole and Albert Bowers were handed 13 years in custody over the manslaughter of the Thames Valley Police traffic officer.
Pc Harper, 28, was caught in a strap attached to the back of a car driven by Long and dragged to his death down a winding country road as the trio fled the scene of a quad bike theft in Berkshire on the night of August 15 2019.
Long – the leader of the group – admitted manslaughter, while passengers Cole and Bowers were convicted of manslaughter after a trial at the Old Bailey.
All three were cleared of murder by the jury, which deliberated for more than 12 hours.
At a hearing in November, Attorney General Suella Braverman said the youths' sentences should be increased, for an offence that was "as serious a case of manslaughter as it is possible to envisage".
Mrs Braverman told the court: "Pc Harper paid the ultimate price for his bravery and this should be reflected in the sentence."
She also said Long, "who was and remains dangerous", should have been given a life sentence.
But lawyers representing Long, Cole and Bowers, who appeared by video-link from HMP Belmarsh, argued that their sentences were "manifestly excessive" and should be reduced.
On Wednesday morning, Dame Victoria Sharp – sitting with Lord Justice Holroyde and Mr Justice William Davis – dismissed the Attorney General's application to increase the trio's sentences.
Pc Harper's widow Lissie, who is campaigning for those who kill emergency workers to be jailed for life, said after the ruling that she felt "let down by our justice system".
In a statement, she said: "I am of course disappointed with this outcome and ultimately feel along with the Attorney General and the majority of our country that these sentences are far too lenient, that they do not reflect the severity and barbarity of the crimes they committed.
"I continue to feel let down by our justice system and the inadequate laws that we have in place."
She added: "My husband was killed in a barbaric way that has seen the nation shocked.
"This single act has rocked the lives of so many people who both loved Andrew and those who have watched from afar the heartbreaking story of his death.
"To take someone's life surely should mean to have your own freedom taken in return. Yet these criminals will see the light of day far, far earlier than they ever deserve to.
"I remain more determined than ever to do what is right and to ensure we see what should have been in place so long ago.
"I know now more than ever the importance and requirement for Harper's Law, which would see those who kill our emergency services heroes receive a life jail sentence."
A spokesman for the Attorney General's Office said: "The Attorney General challenged the sentences given to Pc Harper's killers as she considered them to be too low, but she respects the decision of the Court of Appeal.
"Her thoughts remain with Pc Harper's family for their unimaginable loss."
In its judgment, the Court of Appeal also rejected Long, Cole and Bowers' appeals against their sentences for manslaughter as being "wholly unarguable".
Dame Victoria said: "Nothing in the grounds of appeal provides any arguable basis for a successful challenge to any of the sentences imposed for manslaughter.
"They were severe sentences for such young offenders, but the applicants had committed a grave crime and their punishments were deserved."
Cole and Bowers had also sought to appeal against their convictions for Pc Harper's manslaughter, but this was also rejected as being "wholly unarguable".
The Court of Appeal did reduce the sentences imposed on the pair for conspiracy to steal, from 38 months' detention to an 18-month detention and training order given their ages at the time of the offence.
However, Dame Victoria said: "This does not affect the sentences for manslaughter and, because the sentences were concurrent, it does not affect the overall length of the sentences."
She added: "The effect of our decision is that all three offenders remain convicted of the manslaughter of Pc Harper and the overall length of their custodial sentences remain unaltered."