All police forces in England and Wales have been asked to search their files over claims that officers altered witness statements following bitter clashes with picketers at what became known as the Battle of Orgreave at the height of the 1984 miners' strike.
The trawl is part of an Independent Police Complaints Commission scoping exercise to assess whether it can proceed with a full inquiry into events before and after the violent confrontation which resulted in the arrest of more than 90 strikers for riot offences.
Investigators have already examined 65 boxes of documents from South Yorkshire Police which was responsible for the policing operation but concluded this archive could "in no way be described as a complete record of events".
Campaigners have grown increasingly frustrated at delays in setting up a fully inquiry into Orgreave.
IPCC commissioner Cindy Butts said investigators were faced with a potentially vast archive store.
"I understand the concern that exists around what occurred at Orgreave and in subsequent court proceedings and I know this remains a sensitive and emotive subject for many," she said.
"The key issues for us to identify are what, if any, complaints have been made previously, what allegations were made, how those complaints were handled and which individual officers were subject to complaint. Additionally, it will be necessary to consider the strategic decisions that were made with regard to the collation, recording and presentation of evidence," she added.
Nearly 10,000 picketers were protesting at the British Steel coking plant at Rotherham, South Yorkshire in June 1984. They were confronted by 5,000 police officers many of whom had been drafted in from other forces around the country. During the stone throwing and mounted charges 123 people were injured including 72 police.
Criminal proceedings against those arrested later collapsed and South Yorkshire Police paid out more than £500,000 to 39 pickets in an out of court settlement in 1991. No officer was ever disciplined.
Evidence of statement altering by South Yorkshire officers produced by the Hillsborough Independent Panel has led to the largest IPCC inquiry into police conduct ever held. A BBC documentary meanwhile recovered police witness statements which it claimed contained identical phrases to describe what they had seen - echoing the allegations levelled at officers in the aftermath of Hillsborough.
Former NUM president Ian Lavery MP, who along with the Orgreave Truth and Justice Campaign is calling for a full public inquiry into what happened, said he had been asking for this action for the past two years. He said the delays were "not acceptable".
"These people are now grandfathers and great grandfathers who were fighting for the cause of the miners. These are honest hardworking people who are quite ashamed of what happened that day. The vast majority have kept absolutely silent about what happened but they look forward to justice and some form of resolution," he said.
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