Hargreaves, which helps retail customers invest in a range of products through its online platform, said on Thursday it would now disclose its performance as one business unit in full-year results, rather than detailing each unit separately.

"The board considers that the disclosure ... whereby the whole business is reported as one unit, better reflects how the group is managed in practice and we intend to report on this basis in the full-year results and thereafter," Hargreaves said.

It also said Chairman Mike Evans planned to step down as soon as a replacement had been identified. The move follows the replacement this year of the company's chief executive officer as well as its chief financial officer.

Both updates took the gloss off a 10 percent rise in assets in the four months to the end of April on the back of market gains and net inflows, helped by new fund and product launches.

Hargreaves shares fell as much as 5.3 percent and were down 2.2 percent at 1,318 pence at 0907 GMT, underperforming a 1.2 percent fall in the FTSE 100 index.

"We would prefer to see fuller disclosures, given the relative importance of Vantage to the business," Liberum analyst Justin Bates said in a note, referring to the company's online investment platform.

RIVAL PLATFORM

The decision came just two days soon after the firm's shares took their worst one-day hit in nearly a year when U.S. asset manager Vanguard announced plans to launch a rival online platform aimed at retail investors, raising concerns it could challenge Hargreaves' dominant market position.

The chairman's planned departure was also noteworthy, said Liberum's Bates, who has a "sell" rating and 1,107 pence price target on the stock.

"We note this will be the third change in senior management in relatively quick succession."

The extent of the share price fall was marked given the company also reported funds under administration of 77 billion pounds, which was above expectations.

Net new business inflows during the period came to 3.3 billion pounds, while market gains added another 3.8 billion pounds. Total inflows over the 10 months to the end of April were 5.6 billion pounds, the company said.

Hargreaves said the performance was driven by a recovery in investor confidence ahead of the end of the British tax year, new fund launches, including one from fund manager Neil Woodford, and government changes to tax-free savings rules.

Flows were also helped by the company's digital marketing efforts, including the launch of new smart phone apps, and a continued trend for clients to consolidate their wealth on its platform.

The company said it added 56,000 new clients over the four-month period, taking total active clients to 932,000.

(Additional reporting by Tenzin Pema; editing by Edmund Blair and David Clarke)

By Simon Jessop