The Ministry of Justice is to be sued by the mother of a five-year-old boy who was murdered by her boyfriend after an inquest concluded that defects in the probation system contributed to his death.

Alex Malcolm died in November 2016 after he was beaten to death in a park for losing a trainer by Marvyn Iheanacho, then 39, who had been released on licence from prison six months earlier after being jailed for assaulting five women.

Alex’s mother, Liliya Breha, said probation officers had not warned her about his violent history or told her that he was barred from having unsupervised access to children under 16.

In September an inquest jury found that a series of errors related to the privatisation of the probation service, introduced by Chris Grayling when he was lord chancellor, had “contributed to the death”. Breha’s solicitors, Birnberg Peirce, are now preparing a claim for damages against the Ministry of Justice .

“The inquest hearing was so traumatic for me,” Breha said. “I relived every detail of the tragedy. At night, I cannot sleep, I have nightmares and have constant images of Alex. I feel so let down by probation. Why was I not told of the previous violence against women and girls? It was their responsibility to keep this monster away from me and the public. They had all my information so there is no excuse for not telling me. I will be taking legal action for these failings.”

Iheanacho was convicted in 2017 of murdering Alex and sentenced to life in jail. In a note written from prison, he said probation staff had been aware of his temper, and issues with drugs and alcohol.

“My probation worker did not do enough to help me settle down again,” he wrote. “Why did my probation officer not inform Liliya? If she had, things might be very different.”

A probation official told the inquest that London staff were overstretched and dealing with an estimated 5% to 10% increase in their caseload.

This was an avoidable murder. The Ministry of Justice must reassure the public that this will not be repeated elsewhere Harry Fletcher, campaigner

A regulation 28 report, issued by the coroner, Andrew Harris, to prevent future deaths, has been sent to the lord chancellor, Robert Buckland, the health secretary, Matt Hancock, and Jo Farrar, Prison and Probation Service CEO. This stated that several factors were to blame, including shortages of probation staff and of approved premises for prisoners on release.

Harris said there “is still a risk that future deaths will occur unless action is taken”. He has given the government and the probation service until 11 December to respond, although this deadline may be extended.

Harry Fletcher, a victims’ rights campaigner, said the coroner’s report was a damning indictment of the way the government had run the probation service.

“There are systemic and individual failings by the authorities. Liliya Breha has a cast-iron case for claiming damages. This was an avoidable murder. The Ministry of Justice must reassure the public that this will not be repeated elsewhere and ensure that the probation service is properly funded.”

Earlier this year the Observer reported that official data showed that the number of rapes, murders and other serious crimes committed by offenders on parole had risen by more than 50% since Grayling’s reforms to probation were introduced in 2014.

Serious further offence reviews – which take place when a convicted offender under supervision is charged with another serious offence – increased from 409 in the year before the reforms to 627 in the 12 months up to April 2018.

Paying tribute to her son after the inquest concluded that he was unlawfully killed, Breha said: “He was my world and my best friend, too. We did everything together. I’m so angry he was taken away from me. Everyone loved Alex. He was caring, kind and loving, and a very sharing child. He was perfect.”

A Ministry of Justice spokesman said: “Our deepest condolences remain with the victim’s family, and we apologise unreservedly for the unacceptable failings in this case. We will respond to any letter sent by the family in due course.”