A miners' union is being investigated by fraud squad detectives over claims that it earned millions of pounds from a personal injury compensation scheme.
The miners' fund is the world's largest personal injury scheme
The allegations centre on the Union of Democratic Mineworkers (UDM), which is dealing with claims from sick miners.
South Yorkshire Police confirmed they are looking into claims that funds from a compensation scheme set up by the government have been misappropriated.
The UDM said in a statement that it was "shocked" to learn of the inquiry.
"We have always acted in the best interests of our members in securing them tens of millions of pounds in compensation for industrial injury," the UDM said.
Officers are examining the relationship between the UDM and solicitors' firms.
The force's economic crime unit stressed that its investigation was at a very early stage.
The Nottinghamshire-based UDM, which has around 1,300 members, broke away from the National Union of Mineworkers during the bitter year-long miners' strike in 1984.
The NUM and a number of solicitors' firms have also been processing claims on behalf of tens of thousands of ex-miners or their families in what has become the world's biggest personal injury compensation scheme.
Labour MP John Mann (Bassetlaw), who has waged a long-running campaign to highlight alleged abuses of the scheme, said he had handed over documents to police last year.
Mr Mann said millions of pounds which had been paid to solicitors involved in dealing with compensation claims should have gone to miners instead.
"I am absolutely astonished at the labyrinth of companies involved in this scam," he said.
"They are feeding off each other at the expense of dying miners and their widows."
Mr Mann tabled a Commons motion on Tuesday calling for the Department of Trade and Industry to suspend its agreement with the UDM and a firm called Vendside, which was set up by the union to handle compensation claims.
The £7.5bn compensation scheme was set up by the government in 1999 and has been paying out to tens of thousands of miners suffering from chronic lung disease and vibration white finger.
The DTI, which has been dealing with hundreds of solicitors' firms to handle the claims, said it would co-operate fully with the police investigation.
The UDM added: "We will be working quickly and fully with any investigation to allay fears over the conduct of UDM officials.
"We are confident that there has been no wrongdoing and we look forward to demonstrating this as part of any investigation."