Ross stood down as deputy chairman of Carphone Warehouse yesterday after admitting he had failed to disclose within the necessary timeframe that he had pledged a large proportion of his stake in the company against personal loans.

Johnson had appointed Ross, hailed by London 2012 chairman Sebastian Coe as one of Britain's most successful businessmen, in May, shortly after he had been elected to replace Ken Livingstone as Mayor.

Ross said: "I reach this decision with sadness, as I have very much enjoyeod making this contribution to British sport.

"Given the present circumstances, and while they are not connected to the Olympics, I must now devote my full attention to my private business interests.

"I also do not wish to distract others from the important work still to do in making 2012 the success I know it will be."

Johnson said: "I appreciate why David Ross feels he ought to stand down from the Board of LOCOG and the Legacy Board of Advisors.

"I understand he has also offered to resign from the Olympic Lottery Distributor.

"He will, nevertheless, be a loss, having played an active and very useful role over the last seven months.

"I am particularly grateful to him for identifying serious issues with the 2012 Olympic Games that needed to be urgently addressed.

"His report into planning the delivery of the legacy of the Games helped the entire Olympic family to focus on a range of pressing concerns, including security, budget and legacy.

"I chose David Ross for his track record in establishing a hugely successful business and for his work on the boards of Sport England, Wembley Stadium and the Olympic Lottery Distributor.

"He had also clearly impressed the Government with his work on the review into the legal aid system and I am immensely grateful for all his advice to me. I wish him well in the future."

Under stock market rules, if a director uses their shares in this way then the company must issue an official statement.

According to Carphone, Ross made the guarantees at various points between 2006 and 2008, but only told the company on Sunday.

Carphone said that Ross had guaranteed 136.4 million Carphone shares - worth £120 million at today's share price - against personal loans without informing the company.

Ross, a former chartered accountant, owns 177 million shares in the firm, a stake of almost 20 per cent, having set it up with schoolfriend Charles Dunstone.

He is estimated to be worth £873 million, making him the 87th richest person in Britain, according to the Sunday Times.