The lord chancellor will not pursue a judicial review of the Parole Board's decision to release serial sex attacker John Worboys, the Ministry of Justice announced this morning. However, David Gauke MP has expanded the government's transparency review to consider how Parole Board decisions can be challenged.

Gauke told the House of Commons that the bar for judicial review to succeed is very high. He said: 'The test for deciding if a decision is unreasonable is not simply that the decision maker – in this case, the Parole Board – could have made an alternative decision, but that no reasonable person would have come to the same conclusion on the facts of the case. Similarly, on procedure it would be necessary to identify a failing to follow that process by the Parole Board that would have had a material impact on the decision.'

After taking legal advice, Gauke decided it would be inappropriate to proceed with a judicial review.

The Parole Board currently has a statutory duty that prevents proceedings being disclosed. Gauke has already begun the process of making parole decisions more transparent. However, he announced today that the review will go further. The terms of reference have been expanded to include consideration of the law, policy, guidance and practice relating to challenges to Parole Board decision-making. The review will consider whether there should be a mechanism to allow parole decisions to be reconsidered and how that can be achieved while retaining the independence of the decision-making process. The review will be completed before Easter.

Gauke acknowledged concerns that the Victim Contact Scheme, operated by the National Probation Service, 'may not have worked as well as it should have in this particular case'. The justice secretary has asked Dame Glenys Stacey, HM Chief Inspector of Probation, to conduct a 'rapid fact-finding exercise' to confirm whether legislative provisions and existing policy and processes were adequately followed. Her findings will inform a 'wider review'.

Gauke stressed that Worboys will not be released until his licence conditions have been finalised. Victims will have the opportunity to make representations on the conditions.

Gauke said he fully supports victims' rights to take their own advice and challenge the board's decision. The Centre for Women's Justice, a charity, has raised over £18,000 of a £50,000 target through CrowdJustice, a crowdfunding platform, to find out why the Parole Board decided to release Worboys.

Harriet Wistrich, a solicitor at civil rights firm Birnberg Peirce and the charity's founding director, said: 'This will be an unprecedented legal challenge. Where a decision appears to be so irrational, as it does in this case given all the known facts, there is an arguable basis to challenge the rules preventing publication of reasons. If we get access to the reasons then we can explore grounds for challenging a decision which is so insulting and horrific for all the victims concerned.'

Following Gauke's statement, London mayor and former solicitor Sadiq Khan said he has informed Professor Nick Hardwick, chair of the Parole Board, that he has instructed counsel 'on a possible judicial review' of the board's decision. Khan said he was astonished and disappointed 'that the government is accepting John Worboys' release without challenge'.