Alleged victims of the serial sex offender John Worboys are ready to bring fresh prosecutions against him and send him back to jail, according to their lawyer.

Women targeted by Worboys are devastated by the imminent release of the black-cab driver, who “denied his heinous crimes and then forced [victims] to endure the torment of a criminal trial”, said Richard Scorer of Slater and Gordon. Scorer represents eight of Worboys’ alleged victims who were not included in the original criminal prosecution.

Q&A Why is John Worboys being released and can the decision be reversed? Show The Parole Board is able to assess the continued risk posed by prisoners based on psychiatrist and prison guard reports at Parole Board hearings that take place around once a year for each offender. Some of the hearings are oral, some of them written.

In November, a three-person panel of the Parole Board directed the release of Worboys, following an oral hearing. He will be released back into society under strict monitoring on a licence period of at least 10 years. Parole Board hearings are held in private and reasons for release are not made public, although a consultation is to be launched on how the body shares its decision-making with the public. The Parole Board is an independent body and its recommendation for Worboys’ release cannot be overturned by the Ministry of Justice. There are examples of Parole Board decisions being challenged by judicial review in the courts, but only when the prisoner has been denied release. Read a fuller explainer on John Worboys

On Friday night the Crown Prosecution Service revealed that while it had prosecuted Worboys for attacks on 14 women, it had dropped cases involving three other women, even though it assessed they “passed the evidential test”, because there were sufficient counts “to enable the judge to impose an appropriate sentence”.

Worboys, 60, has spent nine years and nine months in prison, including time on remand. He was given an indeterminate sentence, which had a minimum term of eight years, for drugging and sexually assaulting 12 women, including raping one of them. He is likely to be freed within weeks.

After he was jailed in 2009, police also told prosecutors about another 19 alleged victims, but the CPS advised that it would be in the public interest only to prosecute allegations of rape.

One victim, who gave evidence against Worboys in his 2009 trial, lambasted the parole board’s decision to let him go. Speaking on condition of anonymity, she led demands for a full explanation as to why he was now considered to be no danger to women. The call was backed by the mayor of London, Sadiq Khan, and the chair of the home affairs select committee, Yvette Cooper.

“For the parole board to find Worboys safe to release after such a short time is shocking, not least because they won’t tell us why,” she told the Guardian. “We need transparency as a matter of urgency. What do the parole board know that we don’t that means he’s no longer considered a serious danger to women?”

A total of 105 complaints against Worboys reached the CPS, but the Guardian understands he was formally protesting his innocence as recently as two years ago. In March 2013 he applied to have his convictions reviewed by the criminal cases review commission, only withdrawing the claim in May 2015.

Timeline John Worboys case Show Victim one drugged by Worboys When she comes to, the victim finds Worboys attempting to put his hand inside her underwear. She reports it to the police Victim two drugged Remembers nothing more Victim three given a drugged drink which she rejects She escapes without being assaulted Victim four drugged Remembers Worboys kissing her, but nothing more. The following day her legs are bruised Victim five drugged Remembers nothing more Victim six claimed she was drugged, but insisted on being taken home without being assaulted. Worboys was found not guilty of administering a drug with intent Victim seven picked up later the same evening. Drugged and sexually assaulted while unconscious, finding her tampon missing the following day. She reports it to the police Worboys arrested Worboys arrested after his cab's licence plate was identified on CCTV from the building where victim seven lived. Released on police bail and no further action is taken Case dropped against Worboys Victim eight drugged and raped She reports the attack to police Victim nine drugged and sexually assaulted She reports the attack to police Victim 10 claimed she was drugged Worboys was found not guilty of administering a drug with intent Victim 11 drugged Remembers finding her skirt pushed to her waist. Later discovers from police that she had been forcibly penetrated with a vibrator Victim 12 drugged and almost certainly raped She goes to the police Victim 13 drugged Victim 14 drugged The court heard she lost a wristband which was later found at Worboys' home. Worboys arrested at 10am on suspicion of repeated sexual assaults Worboys charged with offences against six women Total later rises to 14 as more victims come forward

Scotland Yard said in statement: “No new information has been received at this time; there is currently no live Met investigation. Should any further information come to light it will be fully investigated.”

The Ministry of Justice declined to comment on whether it would change the law to allow details of parole decisions to be released, and the political fallout of the case looked likely to spread to Theresa May. The prime minister has backed the police against two of Worboys’ victims in a continuing supreme court battle over police blunders in their investigations, which is due for a ruling within weeks.

As home secretary, May intervened to support Scotland Yard’s case that it should not be held liable under the Human Rights Act for its failings.

Two of Worboys’ victims had already won an appeal court ruling that police failed to carry out an effective investigation. Even though he drove one of those victims to a police station, having been persuaded to do so by another man, officers dismissed her as a drunk and failed to take Worboys’ name or car registration. The other victim, who had been drugged and raped, went to police but they did not even log it as a serious sexual assault.

The human rights organisation Liberty said May “has serious questions to answer” about her backing of the police.

The parole board is meanwhile facing anger over the decision to release Worboys, and for the failure to inform all his victims before the announcement was made.

Parole board chair Nick Hardwick has apologised ‘unreservedly’ over the fact that some victims were not informed of the decision to free John Worboys. Photograph: HM Inspectorate of Prisons/PA

Nick Hardwick, who chairs the board, apologised unreservedly because two victims had not been informed of the decision, but pointed out that it was the role of the probation service’s victim contact team to pass on the information.

Hardwick defended the decision, saying the law prevented any publication of the three-person panel’s decision-making process. However, he said the case highlighted the need for greater transparency and that he had “radical plans” to change the rules.

He has been called to explain the parole board’s decisions to the Commons justice committee. Robert Neill, who chairs the committee, said: “In my view it is ridiculous that the current rules prevent the board making public the reasons for their decisions.”

Scorer is representing women who successfully sued Worboys in the civil courts, but were not included on the indictment in his 2009 trial, even though they gave statements to the police.

He said the question of whether Worboys had admitted his crimes was crucial. “If he still denies his crimes, then he clearly poses a continuing risk to women,” he said. “If he now admits that he deliberately and systematically drugged and raped women, then the police need to look at whether there are any crimes that he was not convicted of and seek justice for those victims.”

Scorer said that when he visited Worboys in jail in 2013 he was “clearly a very manipulative and dangerous individual” and that he was “concerned [Worboys] may have fooled the board into believing he is no longer a threat”.

Keir Starmer, who was the director of public prosecutions at the time of the conviction and is now a member of the shadow cabinet, said: “It is very important that if there are any allegations anybody thinks have not been looked into sufficiently, they go to the police.”