The Home Office has failed to grant visa extensions to allow the children of a victim of the Grenfell Tower fire to allow them to attend the public inquiry into the death of their mother and 71 others, saying they had to prove they needed to be there.

Mohammed Samimi, from Iran, said that he and his sisters, Zhara and Maryam, have not had their applications for extended visas approved even though they expired last year.

In September they buried their mother, Fatima Afraseiabi, in Mortlake cemetery. She was staying with her sister, Sakineh Afraseiabi, on the 18th floor of Grenfell Tower on the night of 14 June 2017 following a family party. Both women died.

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In April, the Home Office wrote to lawyers for the deceased’s three children requesting “evidence of a requirement to attend [the inquiry] in person”, which the lawyers insist is not appropriate. The children are recognised by the inquiry as core participants and wish to attend, regardless of whether the inquiry demands it or not.

Samimi said that he had raised the issue in person with Nick Hurd, the Home Office minister with responsibility for the victims of Grenfell Tower. The family’s lawyers said they want to attend the inquiry “to ensure that all matters are properly and fearlessly investigated”.

They said: “In our experience, questions posed by bereaved families assist significantly with uncovering the circumstances of their loved one’s death. Our clients’ ability to remain fully involved in the inquiry proceedings would be significantly hampered if they were unable to remain in the UK.”

The three siblings were originally granted three-month visas and have applied for those to be extended to six months. Samimi runs a photographic and video business in Iran as well as having property interests.

He said he needs to return to look after problems that have developed since September, while he has been in the UK. He said he has lost his business, and has not been able to pay debts or his staff.

“The hardship from losing my business after building it up for 17 years has only compounded the suffering I have felt from my mother’s death,” Samimi said.

Our priority has been to ensure the survivors of the Grenfell Tower tragedy receive the support they need' Home Office spokesperson

On Tuesday, the Home Office issued new guidance that it said will allow people with core-participant status to extend their stay in the UK for a further six months.

The ministry said: “This is to provide certainty for relatives that they will be able to remain for the anticipated period of the inquiry’s oral evidence sessions.”

However, their case remains unresolved and lawyers for the bereaved say six months is too short. The inquiry is set to last until 2020.

A Home Office spokesperson said: “The Grenfell Tower fire was an unimaginable tragedy that should never have happened. Our priority has been to ensure the survivors of the Grenfell Tower tragedy receive the support they need. Requests from the family members who are visiting the UK to remain in the UK for the inquiry are under consideration and are being expedited.

“We have always been clear that we will do everything we can to make sure that relatives who are required to provide evidence in person, or need to be in the UK to participate in the Grenfell Tower inquiry, are able to do so.”