Sweeping new powers must be given to social tenants as part of an overhaul needed to ensure a Grenfell-style disaster never happens again, a powerful cross-party commission will warn this week.

It found that social tenants are being failed by a system that leaves them waiting an average of eight months before their complaints are investigated, even when their safety could be at risk.

The calls for a once-in-a-generation rethink of tenants’ rights come from the Social Housing Commission, a year-long investigation brought together by the charity Shelter following the Grenfell Tower fire in which 72 people died. Its commissioners include the former Labour leader Ed Miliband, the Conservative former cabinet minister Sayeeda Warsi and the campaigner Doreen Lawrence, whose son Stephen was murdered in a racist attack in 1993. Lawrence said few people in positions of power “understand what this experience [being a social tenant] is like”.

“I doubt they’ve ever had to live in poor housing or know what it is like to feel invisible, like no one cares,” she said. “The case for investing in social housing is overwhelming. We cannot solve the housing crisis without it, but the system must be made more responsive to tenants at the same time.”

The commission is demanding a regulator with similar muscle to the body set up in the aftermath of the financial crisis to fix a system that has left social tenants feeling ignored or branded as troublemakers for raising serious concerns. The panel is also calling for a “significant expansion” of new social housing as well as comprehensive changes to the way the sector is run. The commission has spent a year researching the housing emergency, with 31,000 people responding to its consultation exercise.

One of the main findings is how the current regulatory system is failing social renters. In 2017-18 the average time taken for a decision by the housing ombudsman was eight months. Deep frustrations were expressed to the commission by both private renters and those in social-rented accommodation. The commission’s full report is published on Tuesday.

Ed Daffarn, a former resident of Grenfell Tower, says councils must be held to account for their failures. Photograph: Sarah Lee/The Guardian

The commissioners – who also include the former Treasury minister Jim O’Neill, Ed Daffarn of Grenfell United, which represents survivors, and Gavin Kelly of the Resolution Trust thinktank – want a new regulator for landlords based on the Care Quality Commission or the Financial Conduct Authority, which was set up after the crisis of 2008 to protect consumers.

Research for the commission by the Britain Thinks agency found that 31% of social renters feel their landlord does not think about their interests when making decisions. In London 38% of social renters feel their landlord does not consider their interests. Nationally only a fifth (19%) of social renters felt able to influence the decisions made by their landlord about their home.

The commission also proposes a new national tenants’ organisation to give social housing residents a voice at a regional and national level and the scrapping of rules that slow down tenants from complaining to a regulator.

There has been growing clamour for an overhaul of renters’ rights after the Grenfell disaster in 2017. The next phase of the official inquiry into the fire is not expected to go ahead until the end of the year.

Daffarn said: “Social housing is not like choosing a doctor – you can’t just up sticks and move if your housing association gets a low rating. Much more is needed to put power in residents’ hands. We need a new regulation system that will be proactive and fight for residents, with real repercussions for housing associations or councils that fail in their duty.”