The actor Ricky Tomlinson, who was one of the building workers imprisoned in one of the most controversial cases involving trade unionists in the past 40 years, is calling for the government to "lift the veil of secrecy" from the case.
Chris Grayling, the justice secretary, has told surviving members of the "Shrewsbury 24" that documents relating to the case will be withheld for a further 10 years. The ban will be reviewed again in 2021.
In a letter to campaigners, Grayling said the documents were being withheld under section 23 of the Freedom of Information Act, a section relating to national security. A Ministry of Justice spokesman said the lord chancellor had renewed the decision made by his predecessor in not releasing remaining papers.
"The majority of papers relating to this case are already available from the National Archives. Where necessary material can be held for longer than 30 years under the Public Records Act."
But Tomlinson said his co-workers were convinced that the Tory government of the time had been behind the prosecutions. He has called for ministers to release all the relevant information.
Tomlinson said: "We were building workers trying to get decent wages and working conditions. What's that got to do with 'national security'? We were convicted for conspiracy in 1972. We knew we were innocent. And now the government continue to throw a security blanket over what really happened … and the role of the security forces. We believe the prosecutions were directed by the government."
The actor, with fellow pickets, will hold a press conference in Liverpool on Monday as the campaign to force the government to release all the relevant paperwork gathers momentum.
The pickets were arrested in 1972 during the first ever national building workers' strike, which lasted 12 weeks and led to a pay rise. But the union's picketing tactics enraged the construction industry and government.
Five months after the strike ended 24 people were arrested and charged with offences, including conspiracy to intimidate and affray. They were convicted at Shrewsbury crown court in 1973 and six were jailed. Tomlinson got two years and Des Warren three years.
Their case became a cause célèbre for the left and unions, which believe the builders were victims of a government plot to make an example of trade union activists who took part in successful picketing.
Last year a letter obtained under the Freedom of Information Act revealed there was discussion at the highest level of the Heath government over the decision to prosecute the men.
In the document, dated 25 January 1973, Sir Peter Rawlinson, the attorney general, told the home secretary, Robert Carr, that the strike had produced "instances of intimidation of varying degrees of seriousness" and that he had to decide whether the men should be prosecuted.
But he said: "The intimidation consisted of threatening words and … there was no evidence against any particular person of violence or damage to property."
Rawlinson said that Treasury counsel, to whom the director of public prosecutions had referred the cases, "took the view that the prospects were very uncertain, and … I agreed with him that proceedings should not be instituted". Despite this assessment, three weeks later the 24 men were charged.
The Tory government had close links with the building industry and was always suspected of being under pressure from that quarter to act.
