Carrie Johnson recalled her fear over black cab rapist John Worboys’ planned release from jail as she spoke in support of the campaign to keep Joanna Simpson’s killer behind bars.

British Airways captain Robert Brown bludgeoned his wife Ms Simpson to death with a claw hammer in their family home in October 2010 as their two young children cowered in a playroom.

The killer was acquitted of murder but admitted manslaughter on the grounds of diminished responsibility and is due to be freed from prison on licence later this year.

Mrs Johnson joined Ms Simpson’s mother, Diana Parkes, on Wednesday at the launch of a campaign aimed at urging Justice Secretary Dominic Raab to intervene to block Brown’s automatic release.

She spoke of her ordeal at the hands of Worboys after he was jailed indefinitely in 2009, with a minimum terms of eight years, and gave evidence against him at his trial.

Speaking on Wednesday evening at Westminster Chapel in central London, she said: “I remember Hetti (Barkworth-Nanton, Ms Simpson’s close friend) and Diana describing themselves as sitting ducks, powerless to do anything, and I knew that feeling from my own experience.

“When I found out the taxi cab rapist John Worboys was due to be released much earlier than we thought, with no explanation as to why, I remember feeling really scared.”

Mrs Johnson described the case as another instance in which “the law was badly letting the victims down and failing to do its job to protect women”.

But she added that, having campaigned for a judicial review of the Worboys case which led to him being kept behind bars, she believed there was hope for change.

She urged Mr Raab to intervene, saying: “Surely, common sense must prevail.”

Mrs Parkes has warned that Brown will be “very bitter” when he enters the community, having lost his job, his high earnings and his children, who she says never want to see him again.

She said on Wednesday: “Most of his life before prison has been stripped away and he won’t be able to contain his anger and will seek revenge.”

The 83-year-old grandmother described the killing as a “life-changing tragedy which has altered my whole family’s life forever, leaving my grandchildren, aged nine and 10, without a loving and caring mother”.

Former prime minister Boris Johnson made a surprise appearance alongside his wife at the event, where speakers also included shadow domestic violence minister Jess Phillips, former Home Secretary Priti Patel and former Justice Secretary Robert Buckland.

Ms Phillips has also thrown her weight behind the campaign, saying it was “unfathomable” that Brown, with his history of domestic violence, would be let out of prison.

The Queen Consort is among others who have supported Mrs Parkes’ wider campaign to tackle violence against women, previously citing her as the inspiration behind her work with domestic abuse victims.

Camilla called last year for more action to address violence against women when she appeared alongside Ms Parkes at Clarence House for Woman’s Hour and BBC Breakfast.

The Justice for Joanna campaign urges supporters to write to their local MP asking them “to put pressure on (Justice Secretary) Dominic Raab to take this case seriously and do the right thing – for Jo, for her family, for all women and girls”.

Mr Raab has invited Mrs Parkes to meet with him next week to discuss the case, which he says he will be reviewing carefully.

Brown, who believed he was “stitched up” by a prenuptial agreement with 46-year-old Ms Simpson, was cleared of murder by a jury at Reading Crown Court in May 2011.

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.

The Ministry of Justice has been contacted for comment.