Some of the UK’s best known mental health charities and the Royal College of Psychiatrists have jointly called for an independent inquiry into the deaths of scores of vulnerable people who were reliant on welfare benefits.

Twenty organisations have signed a statement highlighting deep concern that shortcomings in Department for Work and Pensions policies and safeguarding processes are linked to avoidable deaths.

The statement reflects growing disquiet over the DWP’s handling of benefit-related deaths after revelations about the case of Errol Graham, a 57-year-old grandfather with severe mental illness who died of starvation after his benefits were cut off.

It says: “As organisations that work with people who need support from the benefit system, we are deeply concerned that some of the policies and processes of the Department for Work and Pensions appear linked to avoidable deaths.

The statement cites a recent National Audit Office (NAO) report which found that although the DWP had internally investigated 69 cases of suicide linked to benefit issues in the last six years, officials had no idea whether the lessons from those cases were ever learned or their recommendations implemented.

It adds: “We are therefore calling on the government to establish an independent inquiry into those deaths where it appears that the welfare benefits system may have been a significant factor, with a remit to recommend changes to policy as well as internal DWP processes where needed.

Organised by Rethink Mental Illness, the statement’s signatories include Mind, Mental Health Foundation, Centre for Mental Health, Disability Rights UK, Macmillan Cancer Support, Liberty, Inquest, Child Poverty Action Group, and the Trussell Trust.

The call for an independent inquiry, which would recommend changes to policy as well as internal DWP processes, reflects waning confidence in the department’s capacity and desire to make improvements to the safeguarding system in an open and transparent way.

Last week MPs on the work and pensions select committee wrote to Thérèse Coffey, the secretary of state for work and pensions, demanding answers to a series of detailed questions about the DWP’s approach to benefit-related deaths.

Its chair, Stephen Timms, said that if it did not receive a satisfactory response it would be “difficult for the public to have confidence that the department is doing everything it can to provide an effective safety net for the people it serves”.

Alison Turner, Graham’s daughter-in-law, welcomed the statement as a show of solidarity with families who had lost loved ones as a result of DWP failures to understand the impact of mental illness on claimants. “The world is now beginning to realise why Errol and many more like him have suffered.”

A DWP spokesperson said: “These are complex and devastating matters that we take very seriously. We always seek to learn lessons where we can and we are urgently working to drive forward improvements in the system. We will carefully consider the NAO’s findings as part of our ongoing work.”

Graham’s family has launched legal action in an attempt to prove that the DWP acted unlawfully and put him at risk by failing to put in place effective safeguards to protect vulnerable benefit claimants.

His emaciated body was found in his flat in June 2018, just months after his benefits – his only source of income – were withdrawn by DWP officials.

A inquest into his death last year revealed that although the DWP’s attempts to contact Graham to inform him his benefits were at risk were unsuccessful, it cut them off anyway. The department did not inform his GP, landlord, family or the police about what it had done. These actions were in line with guidance, it said.

Although the DWP has announced that it is to set up a serious case panel to investigate benefit deaths, very few details are known about its terms of reference, or this will be a closed, internal body consisting of senior civil servants that will meet just four times a year.

• In the UK and Ireland, Samaritans can be contacted on 116 123 or email jo@samaritans.org or jo@samaritans.ie. In the US, the National Suicide Prevention Lifeline is 1-800-273-8255. In Australia, the crisis support service Lifeline is 13 11 14. Other international helplines can be found at www.befrienders.org.