The fate of David Ross remained in the hands of JPMorgan’s private banking unit last night after it emerged that the mobile phone tycoon had pledged his plunging wealth to service huge loans from the investment bank.

It is believed that the loans were taken out last year to fund a spectacularly ill-timed bet on the commercial property market. As the value of both Mr Ross’s shares and property plunged, the Conservative Party donor was forced into a deadly spiral where he had to promise more and more assets as collateral to JPMorgan just to cover the value of his loan.

Mr Ross borrowed heavily – sources estimate the figure to be in excess of £100 million – and now could be forced by JPMorgan to sell off his investments and country estates so that the bank can get its cash back.

This could mean a firesale of Mr Ross’s 19.4 per cent stake in Carphone Warehouse, the company that he co-founded with Charles Dunstone two decades ago, and properties such as Nevill Holt, in Leicestershire, which plays host to the Grange Park Opera.

On Monday, it emerged that Mr Ross had mortgaged his entire £200 million portfolio of shares across four companies without telling any of the companies concerned – a breach of Financial Services Authority rules. Company directors are obliged to disclose any share dealings they make.

The property and private equity assets that Mr Ross bought with the loan could not easily be cashed in.

One friend said that the loan was intended only as short-term bridging finance. It was originally pledged against only the Carphone shares but, as their value plummeted over the past few months, JPMorgan required him to mortgage more of his investments.

City sources say that later he added his stakes in Big Yellow, the storage group, National Express and safety group Cosalt, a company with which his family has a 50-year connection. As the value of each investment fell with the stock market, the bank required more and more collateral.

Carphone insiders said that Mr Ross had agreed with JPMorgan over the weekend that he could publicly declare that “none of these loans is currently in default” – meaning that he was meeting his interest payments – and that “he had no current intention to sell any of his shares in the company”.

Charles Dunstone, Mr Ross’s lifelong friend and Carphone Warehouse chief executive, said: “The key thing is that he said in his statement I have no intention of selling my shares. He could not have said that if that was not the case. That statement was approved by his banks. That’s why it was so important he gave that undertaking and we could pass it on to people.”

Mr Ross continued to lie low yesterday. However, on Monday he appointed Osborne Clarke, the law firm, to help him with the legal ramifications of a Financial Services Authority investigation into the affair.

On Tuesday he appointed public relations consultants to help him to deal with the crisis, although they declined to answer questions about his finances or provide any additional information beyond statements released by Carphone Warehouse and National Express.

It is believed that JPMorgan could, in theory, force Mr Ross to sell anything he pledged as collateral if he breached the terms governing the loan. Those conditions have not been made public, but the collapsing value of his investments means that more collateral has been required. Last night Carphone Warehouse shares fell nearly 5 per cent to hit a five-year low, reducing the value of his shareholding in that business by £7 million to £150 million. If JPMorgan was to sell Mr Ross’s assets at firesale prices, he would lose millions. At its height, Mr Ross’s empire was valued at £900 million, but he could be left with only 10 per cent of that.

A separate property business, Kandahar, backed by Mr Ross in partnership with Morgan Stanley, which owns a string of high street developments, is also struggling. It owes money to HBOS, the part-nationalised bank, and is understood to be in breach of the conditions attached to the lending. HBOS has recently reviewed the portolio but decided not to pull the plug on the business.

The borrowings are not personally guaranteed by Mr Ross so HBOS has no recourse to his assets. But Kandahar, which owes HBOS nearly £500 million, formed a large part of Mr Ross’s asset portfolio. Morgan Stanley’s real estate fund believes that it will lose money on the deal and Mr Ross’s investment could now be worthless.

There was support for Mr Ross from his friends yesterday. Hugh Osmond, the former PizzaExpress owner, said: “I completely support David and I don’t think he has been given enough credit for, with Charles, building one of the great businesses of its generation. Carphone is one of the best start-from-the-bedroom companies ever.”

Mr Ross resigned from his position as Olympics adviser to Boris Johnson, the London Mayor, and as chairman of National Express on Tuesday. He had mortgaged his holding without telling the company. He is also expected to have to forfeit his remaining City directorships, including that at Big Yellow. Cosalt is considering dropping him as chairman. John Carl Ross, Mr Ross’s grandfather, was chairman when the company floated in 1971 and his father John was chief executive until he resigned in November 1986 over a fall in profits.

JPMorgan, HBOS and Morgan Stanley all declined to comment.

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