The Financial Services Authority (FSA), the City regulator, is threatening to name and shame or fine short-sellers that fail to disclose their bets against the UK financial services sector in the wake of last week's ban, it emerged today.

The stance came amid fresh shareholding disclosures by investors including a £292 million short position in HSBC held by Eton Park, a hedge fund set up by former Goldman Sachs bankers.

Eton Park revealed that it had taken a short position equivalent to 0.28 per cent of HSBC's market value, last night set at more than £104 billion.

Eton Park said the holding was held as of yesterday. It declined to comment beyond the terms of its disclosure.

The financial regulator told Times Online that it would allow hedge funds and other investors a day or two's grace to ensure their disclosures were in order.

But, after that, the FSA said it would pursue errant investors.

"They would be subject to directives on market abuse. We could impose an unlimited fine or public or private censure," a spokeswoman said.

She declined to be drawn on exactly when the FSA would draw the line but signalled it was prepared to move quickly, particularly when it involved highly price-sensitive shares.

The FSA imposed a four-month ban on short-selling against the financial services sector late last Thursday after unprecedented turbulence hit the shares of banks, insurers and fund managers. Some 32 named companies are protected from the speculators.

Funds with an existing short position worth more than 0.25 per cent of the market value of a company are not able to add to their exposure but must nevertheless dislose their positions to the market by 3.30pm each day.

The FSA said today that it also expected investors to inform the market once they had unwound a holding.

Sources close to several hedge funds said they were surprised that more revelations about short position-taking had not emerged. They speculated that the complexity of some investment bets made it hard to establish the exact size of the short holding.

Fluctuations in share prices would regularly alter a fund's position, making it extremely hard to track the disclosable exposure, they said.

The regulator's move came as Deutsche Bank and AQR Capital Management emerged with late declarations about their positions in Friends Provident, the insurer, and Investec, the South African investment bank, respectively.

Short-sellers sell borrowed shares in a company in the hope of making a profit by buying them back more cheaply at a later date.

The practice, while legal, has created a furore, with critics accusing hedge fund "spivs and speculators" of helping to bring some of the UK's biggest banks to their knees.

Man Group, the $79.5 billion listed hedge fund which is not on the protected list, today played down the potential impact of the ban on its own strategies.

It said it had allocated 14 per cent of its assets to long/short strategies, which will be hit under the new regime, compared with the market average of 33 per cent.

It said its $24.7 billion AHL managed futures funds were not expected to suffer from the ban. AHL Diversified Futures, a barometer of the funds' performance, is up 2.3 per cent for the year to date, it said.

It is understood that Man has asked the FSA if it can go on the list.

Man's top executives waded into the company's shares today. Peter Clarke, the chief executive, spent £198,508, buying 49,820 Man shares at 398.45p each.

Kevin Hayes, the finance director, bought 26,768 shares at the same price this morning.

Man's shares jumped 11.5p to 409.5p.

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