A senior member of the International Olympic Committee has claimed that London only won the bid for the 2012 Games because of a misplaced vote.
Alex Gilady said the mix-up happened when a vote was cast for Paris instead of Madrid, which meant the Spanish capital lost out in the penultimate round.
It is understood that the member who was alleged to have pressed the wrong button was Greek IOC delegate Lambis Nikolaou.
Mr Gilady told BBC News 24 that had the vote gone to Madrid it would have finished level with Paris on 32 votes apiece.
The Israeli member of the IOC's London 2012 Co-ordination Commission suggested the Spaniards would have triumphed in a head-to-head with the French, and then would have seen off London in the final round.
Referring to the third round of the voting exchanges in Singapore in July, he said: "London was ahead, but Paris and Madrid were 33-31 in the votes.
"Let's say what we think now happened, that one member made a mistake and voted for Paris rather than Madrid. If he had voted for Madrid it would be 32-32. We would have to have had a vote-off.
"In the vote-off all the votes supporting London would go to Madrid, because the fear was that Paris had a big chance to win."
Mr Gilady claimed that all the votes from an eliminated Paris would then have gone to support Madrid in the final. In the final round of voting, London beat Paris 54-50 to win the right to host the 2012 Olympics .
Feliciano Maroyal, the chief executive officer for the Madrid 2012 bid, told the British newspaper the Times: "We were very close to winning. We can never know if the Greek vote would have been decisive, but it is lamentable for one human error to have ruined all our hard work which we put in trying to win the Games."
A spokeswoman for London 2012 quoted in the same newspaper said: "There are a lot of folklore stories about who voted for whom. At the end of the day, it was a secret ballot. This is the opinion of one individual. The result is what matters and we are not going to be drawn into speculation."