Doubts over the future of Humberts have emerged as the estate agency has been threatened with a winding-up petition.

John McLean, the recently appointed executive chairman, said he believed that the petition would not succeed.

Jonathan Vandermolen, a businessman who sold his company Blenheim Bishop to Humberts for £2.3 million in 2006, claimed that he was still owed more than £1 million from the sale. He has sent a solicitor’s letter to the company threatening it with winding-up proceedings if he is not paid, according to a report in Estates Gazette.

Mr McLean said that the £1 million was payable only if Mr Vandermolen had earned it while working for Humberts under the terms of the sale.

The AIM-listed company has been the subject of takeover speculation for several months. It is understood that its management will make an announcement about a restructuring in the next few weeks.

Humberts made a post-tax loss of £17 million in the year to September 30 after an £18.4 million writedown in the value of the assets that it had acquired in the previous few years.

Management blamed the slowing property market, the credit crunch and the introduction of home information packs for the loss. Humberts’s turnover rose by 135 per cent to £31.9 million last year.

Humberts has 80 offices with 714 staff in the South of England. Its share price plunged in January when it issued a profit warning and Tim James, the executive chairman, and Max Ziff, the chief executive, who had driven much of the aggressive acquisition programme, resigned. Shares have fallen from about 60p in September 2007 to just over 7p yesterday.

Meanwhile, management at John Charcol, one of Britain’s biggest independent mortgage brokers, are in the final stages of deciding whether to sell or refinance the troubled business. It is thought that the private equity-owned mortgage company would sell for about £50 million.

The company’s auditor said last month that it faced a “material uncertainty” about its ability to keep operating, as its total liabilities exceeded its total assets by £532,000.

Gleacher Shacklock, the investment bank, is advising John Charcol on its financing and ownership options.

The business was sold for £100 million in 2000 to Bradford & Bingley, which sold it back to the new consortium at a loss in 2005.

A spokesman for John Charcol said: “As far as I’m aware it’s all OK and nothing’s changed.”

Ian Kennedy, the company’s chief executive, said last month: “We’re not in trouble at all.” Mr Kennedy believes that John Charcol would perform well in a downturn because people would need more advice on mortgages.

John Garfield and Charles Wishart, who founded the business in 1974, and Jon Moulton, the private equity specialist who owns 15 per cent of the company, have ploughed an extra £1.5 million into the company. Investors have also deferred loans of £820,000 until later this year. Last year, John Charcol advised on £4 billion of new mortgages.

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