Police footage of the Hillsborough football ground on the day of the 1989 tragedy may have been deliberately edited, according to a barrister for families who lost relatives in the disaster.

Pete Weatherby QC, representing 21 bereaved families at a court hearing in London considering procedures for the new inquest into the deaths, asked that an independent expert be appointed to examine the film.

Weatherby said an initial view from an expert for the families who had viewed the film suggested it may have been tampered with. There were apparent differences in the way the film, shot from a police handheld camera, cut to different scenes on the day. Much of it was also of poor quality, Weatherby said.

"I would submit an expert should look at this to ensure they are the best possible copies," he said.

The call was echoed by Sam Leek QC, representing Operation Resolve, the new police investigation into whether manslaughter or other criminal offences were committed by South Yorkshire police, Sheffield Wednesday football club, the Football Association or other parties or individuals responsible for Hillsborough.

Leek said the "provenance" of all film and audio-visual evidence was difficult to establish almost 25 years on, and also argued an independent expert should be appointed by the coroner to examine it.

The quality and provenance of police evidence relating to Hillsborough is hugely significant due to the families' assertion that South Yorkshire police covered up their culpability for the disasterincluding by amending and editing junior police officers' statements. Families of the 96 victims have maintained deep suspicion over film and CCTV evidence throughout their campaign, after it emerged that two video tapes of CCTV were stolen from the locked control room at Hillsborough on the night of the disaster. No one was ever caught or convicted for that theft.

At the pre-inquest hearing, four former senior South Yorkshire police officers who were involved in the editing and amending of statements, applied and were accepted by the coroner, Lord Justice Goldring, as parties to the inquest.

Chris Daw QC, representing retired police chief superintendents Terry Wain and Donald Denton, said they were "responsible for gathering and presenting South Yorkshire police's case" after Hillsborough. "They are adamant the work they undertook was not in any sense a cover-up," said Daw.

The Independent Police Complaints Commission, which is investigating the alleged cover-up and possible offences of perjury and perverting the course of justice by police officers after Hillsborough, said it had interviewed 57 of 220 surviving officers whose statements were altered.

Goldring, while acknowledging the huge scale and complexity of the evidence relating to Hillsborough and its aftermath, insisted that the inquest would start on the planned date of 31 March next year.