Robert Brown bludgeoned his estranged wife to death with a claw hammer at the family home in 2010, while their children cowered in a nearby room, and then wrapped the 46-year-old in plastic sheeting and buried her in a pre-dug grave in Windsor Great Park.

The former British Airways captain was acquitted of murder the following year, but admitted manslaughter on the grounds of diminished responsibility.

He is due to be freed from prison on licence later this year, without facing a parole hearing or a mental health assessment, after serving half of his 26-year-sentence.

Joanna Brown was killed by her estranged husband Robert Brown at their home in 2010

The victim’s mother Diana Parkes is running a campaign to keep the killer behind bars, and she has asked Justice Secretary Dominic Raab to intervene and block his release.

Ms Parkes, who raised Joanna in York, said: “He’s dangerous, not only to our family and Jo’s friends but also to the public in general.

“The way he killed Jo – with 14 strikes of a clawhammer when his children could hear – that has to be a man we should be very concerned about coming out of jail.”

The Minister is considering whether he should refer the case to the Parole Board, to decide whether it is safe to release the killer, after he met with Ms Parkes earlier this month.

British Airways captain Robert Brown, who bludgeoned his 46-year-old wife Joanna Brown to death with a claw hammer in their family home in October 2010 as their two young children cowered in a playroom. He is due for release later this year.

He promised to review the case “very carefully”, before announcing his decision in September, and said it is his duty “to keep dangerous offenders behind bars”.

Ms Parkes is urging people to write to their local MP and ask them to “put pressure” on the Justice Secretary to “do the right thing” and block the killer’s release.

The family have been told that Brown is classed as a “critical public protection case”, which means the Probation Service will be required to conduct additional monitoring if he is released on licence.

However, Ms Parkes has little confidence in the service, after HM Inspectorate of Probation found that “chronic staff shortages” are “severely hampering” its ability to protect the public.

Joanna Simpson's mother Diana Parkes, Carrie Johnson and Priti Patel in Westminster, London, for the launch of a campaign to prevent release of killer Robert Brown.

“He committed such a heinous crime and was not properly sentenced. He should be serving a life sentence,” she said.

“Jo was absolutely wonderful. Everybody loved Jo, except her husband. She was a very, very special person and she was a wonderful mother.”

Ms Simpson had filed for a divorce before she was killed, claiming that she had suffered abuse and harassment.

Brown was acquitted of murder at Reading Crown Court in 2011, after the jury accepted that a condition known as “adjustment disorder” had substantially impaired his ability to exercise self control

But he was sentenced to 24 years for manslaughter and a further two years for an offence of obstructing a coroner in the execution of his duty.

Sentencing Brown, Judge Mr Justice Cook said he clearly “intended to kill” his estranged wife and “intended to conceal the body and to hide the evidence of the killing".

During the eight-day trial, the jury was told that Brown had become consumed by anger and resentment before the killing, because he believed he was not getting the divorce settlement he was entitled to.

You can find out how to support the campaign here.

Joanna Simpson's mother: Her killer is still dangerous and must not be released this year