The Hillsborough families have backed calls for Boris Johnson to cancel his appointment of a Grenfell inquiry panelist found to have links to the company that made the combustible cladding.

Margaret Aspinall, the chair of the Hillsborough family support group, criticised the prime minister’s selection of Benita Mehra as “absolutely ridiculous”, after the Guardian revealed she led a charity that received £71,000 from the Arconic Foundation, the charitable arm of the company that made the panels that were the main cause of fire spread.

Mehra, an engineer and one of two experts due to sit alongside the inquiry chairman, Sir Martin Moore-Bick, when the inquiry’s hearings restart in nine days, declined to comment. The inquiry insisted her former role “does not affect her impartiality as a panel member”.

“The families have a right to say we are not accepting this.” said Aspinall, warning of the danger of a repeat of the decades-long search for truth endured by the families of 96 Liverpool fans who died in a crush at a 1989 FA Cup semi-final.

“How can we get to the truth when there is someone on the panel with this association? I would hate for them to go through what we had to go through, but it looks like it is going to happen.”

Between 2015 and 2018, Mehra was president of the Women’s Engineering Society charity when it received a grant from the Arconic Foundation. Arconic made the panels, which the inquiry has already concluded were the primary cause of the spread of the fire that claimed 72 lives at Grenfell.

Facebook Twitter Pinterest Benita Mehra. Photograph: Jeff Spicer/Getty Images

Aspinall’s intervention added to growing pressure on Johnson before the inquiry restarts hearings with sessions examining the selection of the cladding panels, their fire-testing, marketing and promotion.

The shadow housing secretary, John Healey, said Mehra’s appointment “undermines public confidence” and should be reversed. The London mayor, Sadiq Khan, said it was a “major blow” for the Grenfell community and Deborah Coles, of the justice charity Inquest, said it was “shameful”.

“Any perception of bias at a time when there needs to be the most searching scrutiny of Arconic undermines trust and confidence,” Coles said. “Yet again, the inquiry process is found wanting and it is those most affected left fighting for an inquiry that can deliver truth and accountability.”

On Thursday night, Johnson told Grenfell survivors and families of the victims he would investigate her appointment. Making a switch before the inquiry is due to restart will not be easy as any replacement will face intense scrutiny and must be able to commit to at least 18 months of hearings.

Mohamed Ragab, whose nephew Hesham Rahman died in the fire, was at the pre-planned meeting with Johnson at Downing Street. He said: “[Johnson] said he had no idea about this woman dealing with this company,” he said. “He said he would have to investigate and find out what is going on.”

In December, the prime minister wrote to Moore-Bick stating: “I am proposing that Benita Mehra, an experienced chartered engineer replace [Professor Nabeel Hamdi, who decided to withdraw]”.

Another source at the meeting said: “I raised the subject of Benita Mehra with him and [Johnson] didn’t seem to know who she is. I told the story from the Guardian and how she accepted the £71,000 donation from Arconic [Foundation] and it was surely a conflict of interest and … she shouldn’t be allowed anywhere near the inquiry. He promised that this would definitely be investigated and that anything that causes us discomfort should not be allowed to happen.”

David Lammy MP, who has long supported the Grenfell community, said the situation was “scandalous”.

“Grenfell survivors are right to describe this appointment as a slap in the face,” the Labour MP for Tottenham wrote on Twitter. “Mehra must stand down so there is no conflict of interest. The 72 who died in the fire deserve justice.”

Before the link to the US firm’s charity arm emerged, Mehra’s appointment had angered some in the Grenfell community. She replaced another expert, Hamdi, who had greater experience of social housing and community relations, which some believe is lacking in the inquiry leadership.

Grenfell United, the group representing survivors and the bereaved that first discovered Mehra’s link to Arconic, has insisted her position represents a conflict of interest and called for her to stand down.

A Cabinet Office spokesperson said there were “robust processes … [to ensure] any potential conflicts of interest are properly considered and managed”.

The link is particularly sensitive because anger is running high among many survivors at the role played by manufacturers of the combustible cladding and insulation materials used to re-clad the tower during its 2016 refurbishment.

The families of 69 victims and 177 survivors are separately suing Arconic and other materials manufacturers in the US courts for wrongful death. It has argued any litigation should take place in the UK. The UK government has also banned the use of such panels on high-rise residential buildings.

Downing Street declined to comment on what Johnson said about Mehra in what it described as a private meeting.

However, it said in a statement: “The prime minister reaffirmed his commitment to getting to the truth of what happened, learn lessons and deliver justice for victims. During the meeting, they reflected on the phase one report of the Grenfell inquiry, and looked ahead to the next stage.”