West Ham and Newcastle United have been raided as part of a huge football tax fraud investigation involving 180 HMRC officers across the UK and France.
Investigators swooped on offices at Newcastle's St James' Park and West Ham United's London Stadium early on Wednesday morning.
Business and financial records, computers and mobile phones were seized in the raids, which also targeted both clubs' training facilities.
Sky News understands Newcastle managing director Lee Charnley, 39, is among a number of people arrested as part of the inquiry into football transfer dealings.
The raid comes two days after Newcastle sealed promotion back to the Premier League, 12 months after being relegated, thanks to a 4-1 win over Preston.
It is reported West Ham are being investigated over their activity surrounding transfers and the involvement of player agents and that the investigation could extend to other clubs.
HMRC said in a statement: "HMRC has arrested several men working within the professional football industry for a suspected Income Tax and National Insurance fraud.
"180 HMRC officers have been deployed across the UK and France today.
"Investigators have searched a number of premises in the North East and South East of England and arrested the men and also seized business records, financial records, computers and mobile phones.
"The French authorities are assisting the UK investigation, have made arrests and several locations have been searched in France.
"This criminal investigation sends a clear message that, whoever you are, if you commit tax fraud you can expect to face the consequences."
West Ham has released a statement on the raids at the London Stadium and its Rush Green training complex, where the first team squad is based, saying the club was "cooperating fully with HMRC to assist their enquiries."
Download the brand new OffTheBall App in the Play Store & App Store right now! We've got you covered!
Subscribe to OffTheBall's YouTube channel for more videos, like us on Facebook or follow us on Twitter for the latest sporting news and content.
