Property magnates Robert and Vincent Tchenguiz have said they are "co-operating fully" after being arrested as part of an international fraud probe into the collapse of failed Icelandic bank Kaupthing.
The brothers released a joint statement confirming their arrest in the early hours of Wednesday and said they were confident of being "cleared of any allegation of wrong-doing".
They are among seven men arrested in the UK after a string of dawn raids across London in connection with the fall of Kaupthing, one of three Icelandic banks that failed at the height of the credit crunch in October 2008.
The Tchenguiz brothers are among the UK's highest-profile entrepreneurs, having amassed a fortune investing in property and leisure.
They said on Wednesday: "We were arrested earlier this morning and are being questioned with regard to matters relating to our relationship with Kaupthing Bank. Both of us are co-operating fully with the investigation and are confident that, once concluded, we will be cleared of any allegation of wrongdoing."
A team of 135 police officers and Serious Fraud Office (SFO) investigators were involved in the raids, with arrests made after two business properties and eight residential addresses were searched in the London area.
Officials from the SFO said those arrested were aged between 42 and 54. Two men aged 42 and 43 were also arrested in a joint operation in Reykjavik, Iceland. The operations relate to the SFO's investigation into the circumstances surrounding the collapse of the banking group.
It announced an investigation into suspected fraud in December 2009 surrounding UK investment in what was advertised as a "high yield" deposit account called Kaupthing Edge.
The SFO said at the time that its investigation would "seek to identify whether misrepresentations or false representations were communicated by the bank in the push to attract UK investors".
City of London Police officers were based at the brothers' multimillion-pound offices near Hyde Park throughout Wednesday morning. A police van was parked outside one of two businesses believed to belong to the pair a street away from the Dorchester Hotel.