Survivors of systemic sexual and physical abuse have asked Police Scotland to send officers to the first public hearings of an unprecedented inquiry.

They have also urged the independent Scottish Child Abuse Inquiry to publish a detailed breakdown of spending after costs soared by more than £2m in the first three months of this year.

And there have been fresh calls to widen the inquiry to include a charity which has worked with more than 1,000 survivors but was denied “core participant” status, meaning it can’t question witnesses or view evidence.

The first phase of public hearings are scheduled to begin at the end of May, almost two years after the inquiry into historical allegations – chaired by Supreme Court judge Lady Anne Smith – was set up.

If witnesses give evidence about ongoing criminal activity the inquiry “may be obliged” to pass this to police, according to its website.

The Chief Constable of Police Scotland is a core participant but survivors’ groups have suggested that officers should also be at all hearings to listen to testimonies.

Alan Draper, who previously advised the Catholic Church on sexual abuse and now speaks for In Care Abuse Survivors (INCAS) – one of the core participants in the inquiry – said: “I would hope that at the public hearings police will attend. It would certainly help, from a survivors’ point of view.

“If it is clear there’s a particular home, and a number of people are repeatedly named by survivors, we would demand that information is acted upon and potential crimes against vulnerable children are investigated.

“Equally, police could themselves have questions to answer if, for example, it emerges officers failed to take appropriate action about historical abuse, in terms of an investigation.”

Janine Rennie, Chief Executive of survivors' support charity Wellbeing Scotland, said: “The police have a role to play, particularly the child abuse unit. Clearly they’re not going to attend each time, which means there may be a gap, and that is a concern.

“I think criminal prosecutions are the way forward because survivors feel they have no access to justice. We need corroboration and if the same individual is named on a number of occasions then Police Scotland would have to take action.

“A number of perpetrators could still be at large. Survivors don’t want to look at systemic failings as much as they want justice.”

Rennie’s charity has been shut out of the inquiry after an application to be a core participant was refused.

“It seems really strange that we have not been included because we’ve worked with 1,100 survivors,” Rennie added. “They said there already were core participants that work with the same survivors, but that is not the case and we have appealed the decision.”

Meanwhile, Draper has questioned the inquiry’s failure to provide a full breakdown of spiralling costs.

The website shows that the total expenditure is £5.7m – up from £3.5m at the end of December last year – and The Sunday Herald understands there is no upper limit.

Draper said: “They’ve spent an enormous amount of money, considering no public hearings have yet taken place. The inquiry has a responsibility to spell out what this has been spent on.

“While the money should be spent, we can’t deny accountability. We would like to see a breakdown on a quarterly basis, not just a headline figure.”

The first public hearings will begin on May 31 and run until July 12. Among the organisations giving evidence will be Quarriers, Barnardo’s and various religious groups including the Sisters of Nazareth, Daughters of Charity of St Vincent de Paul and the Church of Scotland.

Experts will also give statements on the legislative and regulatory framework governing children in care, the early development of care services in Scotland, societal attitudes towards children and the nature and prevalence of child abuse in Scotland.

Alan Draper of INCAS said: “Lady Smith has invited a wide range of organisations to come. Whether they’ll acknowledge the abuse that happened in establishments they had responsibility for, I don’t know.

“A lot of organisations will be tentative, in terms of publicity. I suspect they’ll be on the defensive. A lot of them have good lawyers and the tendency may be to admit nothing and deny everything.

“What survivors experience is obstruction from organisations, but we’re hopeful this inquiry will open doors so that there will be true accountability.”

David Whelan, spokesman for Former Boys and Girls Abused (FBGA) in Quarriers homes, said a reference group should have been set up by the inquiry to “allow survivor groups to collectively raise any concerns and also to have a better understanding of the inquiry process in laymen’s terms”.

Whelan added: “Some survivors are still raising concerns about barriers – including understanding the legal documents – [which] may be preventing engagement with the inquiry. The Scottish Child Abuse Inquiry process is clearly a legalistic process and many survivors are having real difficulty understanding the legal documents and their concepts. To someone who is non-legal these documents are difficult to understand. Any barriers – perceived or otherwise – encountered by survivors to engaging with the inquiry should be addressed as a priority.”

A spokesman for the Scottish Child Abuse Inquiry said: “This inquiry is one of the most far reaching to have taken place in Scotland and its investigations are progressing.

“Evidence has already been gathered from many survivors through private sessions across the UK, and we continue to source information and documents from various institutions and organisations as we prepare for the first public hearings at the end of this month.

“Each week survivors get in touch with us, and we would encourage anyone who believes they have relevant information to contact us.”

The Sunday Herald also contacted core participants in the inquiry for comment.

Viv Dickenson, Director of Children and Family Services for CrossReach, the Social Care Council of The Church of Scotland, said: “As an organisation invested in continuous improvement we will be interested in the findings of the Scottish Child Abuse Inquiry, which will examine practice as far back as the 1930s, and anything we learn during this process will be used to help us strengthen and improve our safeguarding policies in the future.”

A spokesman for Quarriers said: “We strongly believe that all survivors have the right to be heard and that Scotland should learn the lessons of its past, however painful, to ensure that all children are treated with love and compassion and have the best start in life.”

A spokeswoman for Barnardo’s said the charity would not “risk any perceived conflict of interest in making comments on issues of importance to abuse survivors”.

The Sisters of Nazareth and The Daughters of Charity of St Vincent de Paul did not respond.

A spokeswoman for Police Scotland referred the Sunday Herald to two paragraphs of a lengthy statement by Assistant Chief Constable John Hawkins, which was published on its website in January 2017.

“Police Scotland fully supports and is fully engaged with the Scottish Child Abuse Inquiry. We are grateful that Lady Smith has granted Police Scotland 'core participant' status.

“As the statutory agency with responsibility for criminal investigation into reports of child abuse and as a major stakeholder in the wider statutory framework regulating child protection in Scotland, we fully expect to have a significant role to play in supporting the Inquiry in fulfilment of its terms of reference.”

When the Crown Office was asked if it was participating in the enquiry, a spokesman for the Crown Office and Procurator Fiscal Service – which is responsible for the prosecution of crime in Scotland – confirmed no application to be a core participant in the Scottish Child Abuse Inquiry was submitted.

He added: “We will respond as necessary when required to do so.”

Anyone wishing to contact the inquiry can call 0800 0929300 or email talktous@childabuseinquiry.scot