The Grenfell Tower public inquiry has been delayed again over demands from companies involved in the disastrous refurbishment that their evidence should not be used to help jail them.

The inquiry into the 2017 disaster that killed 72 people was due to restart on Monday after a three-week postponement but will not restart until at least the beginning of March.

The second phase of the inquiry investigating how the council block was refurbished began on 27 January but was halted after little more than a week.

Corporate witnesses including cladding contractor Harley Facades and building operator, the Kensington and Chelsea Tenant Management Organisation, requested an assurance that prosecutors will not use their oral evidence against them to bring criminal charges against individuals or their firms.

An additional delay was triggered last week when the attorney general, Suella Braverman, who must decide whether to give the undertaking, raised fears that the way the demands are phrased could “create real practical challenges for the investigation and potential prosecution of any criminal offence arising”.

The latest delay makes it increasingly likely the inquiry will not publish conclusions until late 2021 or even 2022.

The original request was branded “sabotage” by some of the bereaved and survivors. However, such requests have been granted in several public inquiries. The Grenfell Tower inquiry agreed to seek the undertaking from the attorney general, amid fears the inquiry could be derailed if key witnesses refuse to answer questions.

However, the attorney general’s office has questioned why companies need the same protection against self-incrimination as individuals. The inquiry responded that it would cause great difficulties if witnesses declined to answer because they feared it might incriminate their employer in a future criminal prosecution.

Detectives are investigating possible crimes, including gross negligence manslaughter, but said they would not send any files to prosecutors until the end of the inquiry.

Braverman also asked for a list of witnesses who might be given the undertaking and the size of the corporate entity they work for.

Despite anger among some survivors, who consider the demand for the undertaking as an affront to natural justice, there are also concerns among their lawyers that if witnesses don’t feel they can speak freely without incriminating themselves or their firms, the inquiry will struggle to learn the truth about the refurbishment’s planning and execution. Without doing so, the police will also struggle to get to the bottom of what really happened, they said.

An inquiry spokesperson said: “The inquiry has received an indication that the attorney general will aim to make a decision regarding the undertaking in the week commencing 24 February 2020. The inquiry hopes therefore to be able to resume on 2 March 2020.”

The inquiry chairman, Sir Martin Moore-Bick had earlier warned against delays because the inquiry is examining building safety issues “that directly affect the safety of the public at large”. He therefore believes his conclusions about what happened at Grenfell need to be drawn as quickly as possible.

On Tuesday, apartment leaseholders from hundreds of tower blocks found to have breached fire safety rules in the wake of Grenfell will rally outside parliament to demand financial help from the government.

The leaseholders are facing bills of up to £100,000 each to fix cladding and other problems that freeholders and developers are refusing to fund. They have been told their homes are unmortgageable and are being charged high insurance premiums.