The Financial Conduct Authority is investigating the build up to Aviva's merger with Friends Life and has asked investment bankers involved in the deal to hand over records.
According to a report by the Financial Times, the conduct regulator is looking into a spike in the share price at Friends Life a month before the £5.6bn deal was leaked last November.
Advisors on the deal have been told to disclose whether they had any contact with any third parties to discuss the merger ahead of its announcement last December, the FT understands.
Friends Life's shares rose about 17% in the month before the deal was leaked to the press in November, having fallen 14% since the start of 2014.
The deal with Aviva was the largest takeover announced last year of a UK-listed company, and at the time, the biggest acquisition of an insurance company in the UK in 14 years.
Speaking at the time, Aviva CEO Mark Wilson described the transaction as bringing together two organisations that fit "with surgical precision".
Friends Life was advised by Barclays, Goldman Sachs and Linklaters, while Aviva used JPMorgan, Morgan Stanley and Allen & Overy.
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