Companies that refurbished Grenfell Tower “killed those 72 people as sure as if they had taken careful aim with a gun and pulled the trigger”, the public inquiry into the disaster has heard.

Witnesses involved in choosing flammable materials for the revamp were also accused of trying to “sabotage the inquiry” after they threatened to stay silent unless they are given immunity from prosecution.

There were groans from survivors and victims on Wednesday after staff at key companies submitted a “highly reprehensible” last-minute legal bid seeking an attorney general-backed guarantee which would stop any evidence they gave being used against them in future criminal proceedings.

Stephanie Barwise QC, for one group of victims and survivors, told the hearing on Thursday the timing of the application “gives the appearance of sabotaging this inquiry”.

The hearing has been told designers, contractors and fire safety engineers had “expressly foreseen” the risks of installing the planned cladding system – which would fuel the rapidly spreading fire in June 2017.

Main contractor Rydon, external wall subcontractor Harley Facades, refurbishment architects Studio E and fire inspectors Exova allegedly knew the proposed cladding in which the 129-flat tower was to be encased would burn and fall off if exposed to fire.

Combustible aluminium composite material (ACM) cladding panels were chosen in 2014 as an alternative to zinc to save up to £454,000 on the £9.2 million Grenfell Tower refit, the inquiry has heard.

Grenfell fire remembered two years on: In pictures Show all 12 1 /12 Grenfell fire remembered two years on: In pictures Grenfell fire remembered two years on: In pictures Campaign group Grenfell United project a message on to the side of a tower block in Newcastle ahead of the second anniversary of the Grenfell fire to highlight the number of blocks that are still covered in flammable cladding, despite the role that it played in the fire PA Grenfell fire remembered two years on: In pictures People release balloons in front of the Grenfell Tower during a vigil to mark the second anniversary of the fire (Peter Summers/Getty Images) Grenfell fire remembered two years on: In pictures Downing Street is illuminated green to mark the second anniversary of the Grenfell fire EPA Grenfell fire remembered two years on: In pictures Kensington Palace is illuminated green to mark the second anniversary of the Grenfell fire Getty Grenfell fire remembered two years on: In pictures Campaign group Grenfell United project a message on to the side of a tower block in Salford ahead of the second anniversary of the Grenfell fire to highlight the number of blocks that are still covered in flammable cladding, despite the role that it played in the fire PA Grenfell fire remembered two years on: In pictures Campaign group Grenfell United project a message on to the side of a tower block in by the Grenfell Tower ahead of the second anniversary of the fire to highlight the number of blocks that are still covered in flammable cladding, despite the role that it played in the fire PA Grenfell fire remembered two years on: In pictures Cards bearing names of victims of the Grenfell fire are attached to a railing nearby to the tower Getty Grenfell fire remembered two years on: In pictures People obersve a memorial during a vigil to mark the second anniversary of the Grenfell fire Getty Grenfell fire remembered two years on: In pictures Campaign group Grenfell United project a message on to the side of a tower block in Salford ahead of the second anniversary of the Grenfell fire to highlight the number of blocks that are still covered in flammable cladding, despite the role that it played in the fire PA Grenfell fire remembered two years on: In pictures The Grenfell Tower is illuminated green to mark the second anniversary of the fire Getty Grenfell fire remembered two years on: In pictures Kensington Palace is illuminated green to mark the second anniversary of the Grenfell fire Getty Grenfell fire remembered two years on: In pictures Downing Street is illuminated green to mark the second anniversary of the Grenfell fire EPA

Sam Stein QC, for another group of victims, told the hearing: “The companies responsible killed those 72 people as sure as if they had taken careful aim with a gun and pulled the trigger.

“Those companies responsible killed when they criminally failed to consider the safety of others.

“They killed when they promoted their unsuitable, dangerous products in pursuit of money and a place within the market, and they killed when they ignored that ultimate client – the people of Grenfell Tower.”

Ms Barwise attacked the suppliers of the combustible insulation and cladding panels, Celotex and Arconic respectively, as displaying an “extraordinary degree of contempt” for residents’ safety by marketing their flammable products.

She said Celotex targeted the 67m west London building as a “flagship” project for its RS5000 insulation, and cynically exploited what one of its bosses called “the smoke of confusion” around building regulations.

It actively promoted the material despite senior executives knowing it should have been recalled after safety tests, she added.

In an email exchange between Celotex and one of its distributors, the firm’s head of technical, Rob Warren, wrote it was “clearly wrong” when an inspector “said it was OK to use any insulation up to 18 metres (59ft), and only above 18 metres did it have to be non-combustible”.

He added: “The fire hasn’t got a tape measure and if it starts at the ground floor it will love to race up the first 18 metres. Just shows the smoke of confusion out there.”

The distributor, Martin Stearne at SIG Technical Services, replied: “Never has the expression ‘smoke and mirrors’ been more appropriate”, and added that “if specifically challenged” he would opt for a different product but “if I’m not challenged it’ll be RS5000”.

Ms Barwise further said Arconic almost doubled its UK sales target for the dangerous cladding used on Grenfell Tower in the years before the blaze after it was given the second-lowest fire safety rating in European tests.

The US conglomerate was accused of trying to offload its Reynobond PE cassette cladding in Britain after it was given a European class E rating, threatening sales on the continent in markets such as Spain.

An email exchange showed the Grenfell Tower project was one Arconic was “confident” it would secure, which Ms Barwise said contradicted the firm’s position it was just a manufacturer which sold a product – saying its distributors “targeted potential contractors in projects”.

Its Reynobond PE panels featured a polyethylene core, which has a heat combustion akin to diesel and close to lighter fluid – and has a high-calorific value compared with other construction materials, Ms Barwise said.

She criticised as “absurd” Arconic’s statement when it said “the tragedy at Grenfell Tower shows the awful consequences which can arise when combustible materials are used in a particular combination and configured in a particular manner”.

She said: “That is not what the fire at Grenfell shows.

“It shows that the use of a thermoplastic with a heat of combustion similar to lighter fuel within any construction is likely to result in an uncontrollable inferno... the dripping, burning droplets will set fire to anything in its path.”

Ms Barwise also criticised the evidence given by the Kensington and Chelsea Tenant Management Organisation (TMO), saying the now-defunct organisation had not acknowledged its “contribution to loss of life”.

A “very significant example” of its negligence was its failure to produce personal evacuation emergency plans for the many disabled residents, she said, adding that with regard to cladding products it “appeared to display concern only for aesthetic qualities”.

A “culture of knowing and wilful non-compliance” also pervaded the fire safety engineers Exova, Ms Barwise added.

The inquiry is due to resume on Monday, and chairman Sir Martin Moore-Bick will hear further legal submissions on the bid for witnesses to receive immunity from prosecution.

Cross-examination had been due to start with architects Studio E.

Jonathan Laidlaw QC, for Harley Facades, said four staff from the company had been interviewed under caution by Scotland Yard over alleged potential breaches of the Health and Safety at Work Act 1974.

He went on: “Those who have been interviewed were interviewed in a way which strongly suggests that further interviews, as one would expect, are to come.

“Those of the Harley witnesses not thus far interviewed have had no indication at all and nor realistically will they receive one that they will not be invited to interview in the coming months or years.”

Scotland Yard is conducting its own investigation into gross negligence manslaughter, corporate manslaughter and health and safety offences, and said in September it had so far completed 17 interviews.

Seventy-two people died as a result of the blaze at the west London block after an electrical fault with a fridge freezer sparked a catastrophic fire.

The inquiry continues.