Britain is probing investment banks over insurer Prudential Plc's

failed $35.5 billion bid for rival AIG's Asian business AIA <1299.HK> last year, two people familiar with the matter said.

The probe, ordered by the Financial Services Authority, would examine the circumstances surrounding the whole process, which left Prudential shouldering costs of 377 million pounds ($620.2 million), one of the sources said.

It is happening. It is focused on the advisors and whether they discharged their duties properly, the other person said, speaking on condition of anonymity.

AIA's parent AIG walked away from the deal last June, after Prudential tried to cut its bid price in a last-ditch attempt to woo shareholders baulking at the massive expense and a $21 billion rights issue.

Prudential Chief Executive Tidjane Thiam -- who had embarked on the deal in his first year in the job -- managed to survive the debacle, though there was pressure for him to go.

The deal was also marred by a last-minute regulatory delay, when the FSA worried the insurer's capital might not be sufficient to withstand stress tests, and the complexity of a deal that involved 22 jurisdictions.

The FSA was now examining the failed deal, the sources said, and the role of the three main advisors: Credit Suisse , JPMorgan and HSBC .

Prudential, the FSA, HSBC and Credit Suisse declined to comment. JPMorgan could not immediately be reached.

The probe is a so-called Section 166 investigation, which could lead to enforcement action by the FSA. In such an investigation, the FSA orders a company to commission a report, normally from a large law or accounting firm.

The Financial Times said lawyers Clifford Chance had been mandated with the investigation. Clifford Chance declined to comment.

(Additional reporting by Steve Slater, Quentin Webb and Karolina Tagaris; Editing by David Holmes)

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