The union's HQ in Mansfield and six other premises in the area were searched by the Serious Fraud Office (SFO) in the raids which took place early on Tuesday morning.
"Warrants were executed on Tuesday in respect of one business premises and six residential premises in the Mansfield area," said a spokesman for the SFO.
"The Serious Fraud Office and South Yorkshire Police carried out search operations as part of their on-going investigation into suspected serious or complex fraud in relation to the handling of miners' compensation claims and to the activities of the company Indiclaim Ltd, also known as Walker and Co Claims Services Ltd."
"No persons were arrested and additional support was provided by officers from Notts Police."
Indiclaim Ltd is owned by Clare Walker, of Todwick, who is also the head of claims at UDM claims handlers Vendside.
Bassetlaw MP John Mann, who has long campaigned on the issue of miners' compensation, said he welcomed the news that the investigation was progressing.
"I am not surprised to hear about the latest developments and repeat my demands for all money taken from claimants to be paid back, irrelevant of whether it was taken legally or illegally," said Mr Mann.
"I am sure if the police have found things they will follow it through to prosecution but we are just going to have to wait and see what happens."
Mr Mann added that this week's raids suggest that this is now a major police investigation.
"I can't recall the Serious Fraud Office being involved in any investigations in this region before and this tells me that this is something really major."
"Up until now the South Yorkshire Police fraud squad have been looking into this thing, but that is a local body but the Serious Fraud Office is a national body based in London."
He said he hoped the police would bring their investigation to a swift conclusion so that those who have done nothing wrong could be cleared while anyone who may have committed an offence could be prosecuted.
"Aside from this I would continue to urge claimants who think they have paid money they shouldn't have to come forward with their papers."
Richard Stockdale of Brooke North solicitors – acting on behalf of Vendside – said the claims handlers had nothing to hide.
"Vendside has nothing to hide and is co-operating fully with the police, to resolve this matter as soon as possible."
"This investigation has absolutely no bearing on the claims handling agreement that Vendside has with the DTI which authorises them to process compensation claims and will have no impact on claims for sick and dying miners handled by Vendside."
"Vendside has already successfully secured over £158 million worth of compensation for over 29,000 miners or their families and will continue to pursue claims on behalf of miners and former miners in their best interests and for their benefit and the benefit of their families."
The Serious Fraud Office is a Government department responsible for the investigation and prosecution of serious and complex fraud.
In July detectives from South Yorkshire Police raided Clare Walker's home and detectives are investigating payments linked to the compensation claims that were made by three solicitors' firms to Indiclaim.
She earned £260,000 a year for a 20 hour week at Vendside, who under the terms of a special deal the union signed with the Government in 1999, has helped the UDM to earn more than £20 million settling thousands of claims for miners and their widows.
Miss Walker and UDM's vice president Mick Stevens – who was closely involved with Vendside – deny any wrongdoing but have stepped down from their posts pending the outcome of the police inquiry.