Around 60 people taking part in the “spycops” investigation into undercover policing walked out of court on Wednesday after calling for the the inquiry chairman to stand down.

Participants cheered as they abandoned the courtroom, and unfurled a banned outside the the Royal Courts of Justice reading: “Tear down the #spycops inquiry’s brick wall of silence” and cheered “Mitting out.”

Phillippa Kaufmann QC, representing the core participants, earlier told the court: “It is now abundantly clear that we simply cannot participate in this hearing in a meaningful way.”

She added: “Our clients are not prepared actively to participate in a process where their presence is mere window dressing lacking all substance and meaning which would achieve nothing other than to lend the process a legitimacy it does not have.”

Victims have criticsed the inquiry’s move to grant members of the Special Demonstration Squad (SDS) – the Special Branch unit which infiltrated political groups between 1968 and 2008, some of whom went on to form intimate relationships with female activists, stole dead children’s names to enable fake identities, and spied on family justice campaigns.

Kaufmann claimed chairman Sir John Mitting’s reasoning for not releasing the names of certain police officers was “scant and largely uninformative” and questioned his suitability to oversee the case.

“We have the usual white, upper middle class, elderly gentleman, whose life experiences are a million miles away from those who were spied upon,” she said. 

A woman known as Cathy, from campaign group Police Spies Out of Lives, said outside the court on Wednesday: “We’ve all been disappointed at the slow rate of progress and the complete lack of disclosure.”

She claimed that Mitting “seems to give more weight to the privacy of the officers” than those who were affected by the undercover activity.

“There are two key questions. What were the cover names, and which groups were spied on? Without those two bits of information it’s nigh-on impossible for people to come forward to say this is what happened to me and my group,” she said.

Campaigners say they want an inquiry led by a panel rather than a single judge, because they believe it would better investigate claims of institutional racism and sexism.

Speaking outside the court Kaufmann said she had asked Sir John to sit with a panel “of individuals who have experience, direct experience, of the matters the inquiry aims to address.

“At the heart of all of this lies race and sexual discrimination, so we want him, my clients want him, to sit with others that have an understanding, through experience of those issues. Because his experience, like many, many judges, is a very narrow one.”

Kaufmann said Home Secretary Amber Rudd had been written to repeatedly by core participants, to “take action in respect of these concerns”, and would need to be involved in any decision to convene a panel.

Blacklisted construction workers and the Blacklist Support Group have been granted “core participant status” in the inquiry because of undercover police infiltration of trade unions.

Spokesman Dave Smith said: “Blacklisted workers who have been kept under surveillance by political policing units were always sceptical about whether the British state investigating itself would truly provide justice.

“Time and again [chairman Sir John Mitting] gives the police the benefit of the doubt, to the detriment of those whose lives have been torn apart by this human rights scandal.

“Tinkering around the edges isn’t going to change things. We have no confidence in Mitting. He must go and needs to be replaced with a panel of experts.”

The inquiry was launched in March 2015 by then Home Secretary Theresa May and began two months later in July. It was set up following a series of revelations about the activities of undercover officers who infiltrated various groups, deceived women into forming intimate relationships and spied on families, including the parents of murdered teenager Stephen Lawrence.

Baroness Doreen Lawrence has backed the walk out, accusing Sir John of preventing her from finding out who spied on her family as they sought justice for her murdered son, Stephen, the BBC reported.

“He is turning what should be a transparent, accountable and public hearing into an inquiry cloaked in secrecy and anonymity,” she is quoted as saying. 

“I want to know the names of the police officers who spied on me, my family and our campaign for justice. The chair is not allowing that, in my view, for reasons which are completely unjustifiable and unreasonable.”

To date the inquiry has cost over £9 million.

The inquiry was due to have been completed this year but is reportedly unlikely to start hearing evidence in public before the second half of 2019.

Some 42 cases have been found where dead children’s names were used to provide cover identities for officers.