Leaseholders risk being “fleeced” by profiteering landlords and builders in the post-Grenfell fire safety crisis, a senior government adviser has warned in comments likely to increase pressure on ministers to finally resolve the problem.

More than four years after the disaster that claimed 72 lives, tens of thousands of leaseholders are being landed with crippling remediation bills exceeding GBP200,000 per household in the worst cases. But Dame Judith Hackitt is urging homeowners to challenge the demands by insisting on a second opinion, warning “profiteering” means “we are making lives worse than need be”.

Hackitt, the chair of the independent review of building regulations and fire safety and a former chair of the Health and Safety Executive, also said that despite revelations of “buck passing” among designers and contractors at the Grenfell Tower public inquiry, builders were still “cutting corners” on new buildings.

“I am in contact with people in the fire service and building control who are telling me they are still having to pull people up for poor practice,” she told the Guardian. “There is a general lack of care for quality.”

Her comments come as the government pushes ahead with building dozens of hospital facilities and aims to build 300,000 homes annually to solve the affordability crisis. They also reflect fears among some leaseholders that remediation works may result in fresh faults. The new building safety regulator does not look set to be fully established until mid-2023.

“We should have gone faster,” Hackitt said. “There are still parts of the industry who are saying we can’t change what we do … they are still using excuses … It is disconcerting for us and it is worrying.”

Hundreds of thousands of leaseholders have been told fire safety defects mean they cannot sell their apartments until works costing an estimated GBP15bn have been carried out. They are furious that the government has only promised to cover GBP5bn of the cost and many developers are refusing to help. Some are facing bankruptcy, others are delaying having children, unable to move job and are developing mental health problems as a result.

Rituparna Saha, the co-founder of the UK Cladding Action Group and a leaseholder at the Northpoint block in Bromley, south London, which has ACM cladding, accused the government of “procrastination, incompetence and cover-up, at the expense of our financial stability and mental health”.

Several highly organised leaseholder campaign groups from across England are planning a national rally in Westminster on 16 September in part to demand a new building safety bill that protects them from costs, something parliament has repeatedly voted against despite pressure from Labour and more than 30 Conservative rebels.

“Morally they shouldn’t have to pay, but what shocks me is the size of some of the bills and whether the problem is being added to by them being exploited,” Hackitt said. “They seem to have no right to challenge what is being prescribed.”

She said she wanted to help them in “not getting fleeced by their landlords”. “The first thing you should do is not just get one survey done, get a second opinion.”

In 2020 the Ministry of Housing, Communities and Local Government (MHCLG) issued an advice note saying owners of all buildings needed to check the construction of their walls for fire safety. This caused valuers and mortgage companies to demand safety guarantees on far more homes than in high-rise blocks over 18 metres. But last month, the government issued a statement following advice from Hackitt and other experts that stated: “There has been a disproportionate reaction to the level of risk in medium and lower-rise buildings.”

Hackitt said the 2020 advice would need to change to require greater “proportionality”.

“We need to get to the bottom of this as quickly as we possibly can, before they pay those bills,” she said. “We need to get the message out there that the [leaseholders] should challenge some of these bills and ask is there any other way of making this building safer.”

A spokesperson for the MHCLG said more risk-proportionate guidelines for fire risk assessors were in development.

“Building owners should make buildings safe without passing costs on to leaseholders – and our new measures will introduce a legal requirement for building owners to prove they have tried all routes to cover the cost of essential safety works,” they said.

“The Fire Safety Act will ensure that all blocks of flats are properly assessed for fire safety risks, with action identified and taken in ways that are cost-effective and proportionate to risk.”