A father who was jailed for the manslaughter of his son, nearly 20 years after he shook him as a baby, has had his sentence reduced by the Court of Appeal.

Jack Doak Mitchell was just four months old when, in May 2001, his then 18-year-old father John Doak shook him and caused him serious injuries in Laindon.

Doak was convicted at Basildon Crown Court in 2002 of inflicting grievous bodily harm upon Jack with intent and sentenced to four years in a young offender’s institution.

Jack suffered a “severe and irreversible brain injury” as a result of the assault and died in March 2016, aged 15, after developing respiratory symptoms linked to the consequences of his injuries.

Doak was initially charged with Jack’s murder, but prosecutors accepted a plea to a charge of manslaughter and he was sentenced to three years in jail at Chelmsford Crown Court in November.

At the Royal Courts of Justice in London on Wednesday, Doak’s barrister David Emanuel QC argued that the sentence was “manifestly excessive” and should be reduced.

Doak, now 38 and formerly of Delgate Avenue, Spalding, Lincolnshire, appeared by videolink from prison as Mr Emanuel told the court Doak “continues to grieve” for his son.

Mr Emanuel also said Doak had previously been told that Jack “had died many years before he did by social services”.

He said Doak had “no idea” he was at risk of prosecution, adding: “Initially, to be told that he was being investigated for murder had a catastrophic effect on him in terms of undermining his mental health.”

Doak “lived from 2017 to 2020 with a murder conviction hanging over his head” and had been “bullied and threatened and provided with no support by his employers”, Mr Emanuel said.

Doak has three children with a woman he married in 2008 and is stepfather to his wife’s three children from a previous marriage, the court heard.

Mr Emanuel said Doak had a nervous breakdown as a result of the investigation and was worried about “whether he was going to lose the children that he had now”.

Giving the court’s ruling, Lord Justice Holroyde said: “Nearly 20 years ago, the appellant, then aged 18, caused a severe and irreversible brain injury to his infant son, Jack.”

The judge – sitting with Mr Justice Martin Spencer and Mr Justice Bourne – said that Jack “died of a chest infection associated with the injuries which the appellant had inflicted”.

Lord Justice Holroyde said Jack “was left severely disabled” by the assault, and suffered from cerebal palsy, epilepsy and learning difficulties for the rest of his life.

The judge also said Jack was “fully dependent and unable to feed himself and had a severe visual impairment”, and that “later in his short life he was to become blind”.

Lord Justice Holroyde said Doak “to his great credit turned his life around” after he left prison and had since only committed a “comparatively minor public order offence”.

In his ruling, the judge said Doak contracted Covid-19 in January while in prison and has “continuing symptoms of that infection”, and has also been prevented from “having telephone or written contact with any of his children”.

Lord Justice Holroyde added: “We accept also that the appellant lived for many years with the burden of knowing what he had done and we accept that he broke down and was greatly distressed when he found out that Jack died.”

He also said it was “very difficult for someone who has served a custodial sentence to be told, many years later, that he is to be prosecuted for a more serious crime”.

Lord Justice Holroyde ruled that the three-year sentence was “manifestly excessive” and reduced his sentence to one of two years.

The Court of Appeal also overturned Doak’s original conviction for causing grievous bodily harm with intent, on the basis of new medical evidence, and replaced it with a conviction for causing grievous bodily harm.