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Fifteen people have been arrested in raids including in Rochdale, Manchester and Bradford.
It's in connection with suspected money laundering worth more than £200 million, HM Revenue & Customs (HMRC) said.
Investigators swooped on addresses in the North West, Yorkshire and Nottinghamshire in the long-running investigation, codenamed Operation Enigma.
HMRC said around 250 of its investigators, helped by officers from a number of police forces, searched more than 20 properties in Rochdale, Manchester, Bradford, Southport and Nottingham.
Seven people - four men and three women - were arrested in Rochdale, aged between 32 and 71; there was one arrest in Manchester, a 31-year-old man; and four men were arrested in Bradford, aged between 27 and 55.
A 50-year-old man was arrested in Southport in the raid, and there were two arrests in Nottingham - both men, aged 43 and 37.
HMRC's deputy director for criminal investigation Alan Lee said: ``Operation Enigma is an HMRC-led investigation targeting money-laundering offences.
``At various stages of the investigation, we have worked closely with colleagues from Greater Manchester Police and West Yorkshire and the Humber police.
``Further details cannot be provided at this early stage, as our investigation is continuing.
``However, our activity today sends out a clear message to those involved in this type of criminality.
``Attempts to launder the proceeds of crime are treated extremely seriously by HMRC, and we will relentlessly pursue any individuals or crime gangs believed to be actively involved in money laundering.''