The Serious Fraud Office has launched an inquiry into the UK arm of US insurer AIG.
The SFO said it is looking into "irregularities" at the group's financial products' division, rather than the insurance operations of AIG.
AIG was the biggest insurer in the world but faced collapse last year amid the credit crisis and was bailed out by the US government.
Director of the Serious Fraud Office, Richard Alderman, said: "We will use our full range of powers to seek information and to speak to those with an inside knowledge of the company's operations."
US authorities are already conducting investigations involving conduct at AIG Financial Products Corp.
The SFO said it will be cooperating with US authorities, the UK's Financial Services Authority (FSA) and AIG in the investigation.
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