Police admit destroying items gathered during the Pike River investigation but say the items held "no value".

Some Pike families are demanding answers as to why police destroyed the evidence from the Pike River mine in 2015. 

Detective Superintendent Peter Read said some items gathered during the Pike River investigation that were assessed to hold no evidential value were destroyed. 

"The items had been available to the Royal Commission of Inquiry and the Department of Labour but were not used. Experts were aware of the items but it was believed they held no value to their deliberations," he said.

He declined to say what the items were.

Dean Dunbar and Bernie Monk, who both lost sons in the 2010 explosion that killed 29 men, are calling for an independent inquiry.

Monk told Stuff it was "damning" for police to destroy any evidence from the Pike River mine. 

Sonya Rockhouse, the mother of one of the men who was killed and another who survived the blast, said she had no concerns about the police destroying the items, which had been available to the Royal Commission. 

"It wasn't anything that could be used as evidence. The police were upfront about it and I have no particular concerns," she said.

"It was stuff you would find in any workplace. As far as I remember there was a rubber glove and a piece of overall from the guys who were working in the drift," she said. 

Rockhouse, who is a member of the Family Reference Group (FRG), which works with the Pike River Recovery Agency, said the families would be meeting police, agency staff and WorkSafe on Saturday for an update on the drift recovery. 

Monk said he left the FRG because he did not want to abide by an agreement the group signed with police. 

He believed it was a confidentiality agreement and he wanted to be able to speak freely to the media and to Pike River families about what he regarded were pressing issues, and release information about alleged failings in the police investigation. 

FRG member Anna Osborne previously said the agreement was to reassure the police and the agency they could rely on the group to handle confidential information in a responsible manner and to ensure sensitive information could be conveyed to the FRG at the earliest juncture and then be made available to families when the "the time is right".

Monk and Dunbar previously clashed with police over what they described as crucial data from the mine's "black box" which police denied existed beyond the first mine explosion on November 19 that year. The police admitted they had data up to December 2 after Pike River Recovery Agency chief executive Dave Gawn informed them the agency had the data up to November 24. 

The encrypted SCADA data is an electronic record of everything happening at the mine, with video footage, measurements of gas levels and electrical activity, and records of phone calls.

Two miners walked out after the first blast, but there was a second explosion five days later. Dunbar and Monk believe the data could hold crucial information about the cause of the second explosion, which effectively ended all rescue hopes. 

Monk and Dunbar had no faith in the new investigation team, "which unfortunately includes members of the original investigation team".

"We have been seeking information from them for over two years and they have consistently delayed and denied evidence exists," Monk said.