The Carphone Warehouse businessman embroiled in a share-selling scandal resigned today as Olympics adviser to the Mayor of London.
David Ross quit the company yesterday after it emerged that he failed to declare the use of £120m worth of shares as backing against personal loans.
Today he tendered his resignation from the Board of the London Organising Committee of the Olympic Games (LOCOG) and as chair of the Legacy Board of Advisers, a spokesman for Mayor Boris Johnson's office said.
Mr Ross, who has donated thousands of pounds to the Conservative Party, emailed the mayor, saying he could not continue in the "present circumstances".
He wrote: "I reach this decision with sadness, as I have very much enjoyed making this contribution to British sport, which has been a lifelong passion.
"However, 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."
Accepting his resignation, Mr Johnson said Mr Ross would be a "loss" to the committee.
He said: "I appreciate why David Ross feels he ought to stand down from the Board of LOCOG and the Legacy Board of Advisers.
"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."
Earlier, Tory leader David Cameron acknowledged that Mr Ross's position was an "issue" for the mayor to deal with.
Mr Cameron, who was pictured in many of today's newspapers with Mr Ross at a 2006 social gathering, said he had made the right decision in resigning from Carphone Warehouse.
"Clearly the issue is for the company and for him and also for the Stock Exchange if he broke those rules," Mr Cameron said after a speech to the London School of Economics.
"And it's an issue for Boris Johnson and, I understand, also the Government to consider what to do next, because I think David Ross does some work for both Boris Johnson and (Olympics Minister) Tessa Jowell.
"But I think in the first instance resigning from the company is the right thing to do and it's a matter for the Stock Exchange what they decide and whether they take it further."
Mr Ross, 43, who co-founded Carphone Warehouse, quit the board yesterday after it emerged that he failed to tell the company, and the stock market, about the mortgaging of his shares.
The shares, part of his 20 per cent stake in the firm, were pledged against separate property investments.
The company's stock fell 4 per cent yesterday in the wake of the announcement.
Carphone Warehouse chief executive Charles Dunstone, who went to school with Mr Ross, said his departure was a "sad occasion" and the board had reluctantly accepted his resignation.
He said he thought Mr Ross's failure to notify the company was an oversight.