A drink and drug driver jailed for causing the death of a teenage girl has had his prison sentence increased by the Court of Appeal after it was found to be “unduly lenient”.

Keilan Roberts admitted four offences relating to the death of 17-year-old Chloe Hayman, who was a passenger in his car when it crashed in the early hours of July 24 last year.

The now 22-year-old Roberts had consumed alcohol, cocaine, ketamine and ecstasy before getting behind the wheel of his Skoda Octavia following a night out in Pontypridd, south Wales.

In June, Roberts was jailed at Cardiff Crown Court for three years and nine months and banned from driving for 10 years.

But at a Court of Appeal hearing in London on Thursday, the Attorney General’s Office (AGO) challenged the sentence as being “insufficient”.

Lord Justice Popplewell, sitting with Mr Justice Lavender and Mr Justice Bryan, ruled on Friday that there had been an “error” in the sentencing judge’s approach and increased the total sentence to five years and three months.

The period of disqualification from driving was also increased to 12 years and seven-and-a-half months.

Cardiff Crown Court was previously told that Roberts, of Rhymney, had not met Chloe before the evening of the crash and offered to take her to her home in Tonypandy after arguing with his girlfriend.

Roberts lost control of his car in the village of Fochriw, with the collision resulting in fatal chest injuries to Chloe who died at the scene.

He later pleaded guilty to four counts of causing death by careless driving while under the influence, with each charge reflecting the substances he had taken.

Judge David Wynn Morgan said in June his sentencing of Roberts was within guidelines but acknowledged it may seem “inadequate”.

In challenging the original sentence, the AGO argued the judge’s approach “did not properly reflect the aggravating factors”.

It said in written arguments these included Roberts driving with “two dangerously defective rear tyres”, drinking alcohol after the collision “in an attempt to frustrate the breathalyser process” and failing “to have any regard to the warnings or concerns expressed by others about his behaviour”.

The AGO also said the judge had “insufficiently” adjusted the sentence to take account of the offender’s levels of intoxication which “were substantially in excess of the specified limit in respect of each of the three controlled drugs”.

The AGO document concluded “the sentence was not just and proportionate to the overall seriousness of the offending”.

Lord Justice Popplewell said there had been an “error in the judge’s approach” in relation to sentencing guidelines and how the case was categorised.

He said the judge was required to place the case at “the highest toxicity level”, because “there was a body of evidence showing substantial impairment of the offender’s driving ability”.

“The levels of the drugs were all in excess of the limit by some margin, and in the case of the MDMA over seven times the limit,” Lord Justice Popplewell said.

He added the sentencing judge could not be “criticised” over how he treated the balance of aggravating and mitigating features of the case.

Jeffrey Jones, representing Roberts on Thursday, said the sentence passed was proportionate, adding: “The effect of this crime clearly is going to be devastating to Chloe’s family. This offender will carry the memory of what he’s done for a very long time and his remorse is genuine.”

At sentencing, the court was told Roberts had no previous convictions and had experienced a “fractured and sad childhood”.

Solicitor General Michael Tomlinson said: “When you get behind the wheel of a car while under the influence, you are not only putting yourself in danger but your passengers and everyone else on the road.

“The court’s decision to increase the sentence should serve as a strong warning that reckless behaviour will be punished to the full extent of the law.”

Chloe’s mother Danielle O’Halloran previously said in a victim personal statement that her daughter’s death had left her “utterly broken”.

She added: “I thought time was meant to heal but this isn’t the case when you lose a child. If anything, it hurts more and more each day.”

Chloe’s stepmother Alix Hayman described Chloe in her statement as a “fiercely loyal” teenager who “lived and loved life”, telling Roberts that he had “torn this family apart”.

She said the family’s loss was “like living your worst nightmare daily”.