As noted a while ago on this site, Visa credit/debit cards have a sponsorship deal for the London 2012 Olympics which ensures that fans who want to buy tickets by card for the games can only do so if they use Visa.
Additionally, Visa credit and debit cards will be the only ones accepted at shops or cash machines at Olympic venues.
Unsurprisingly, some people are of the view that this is an unfair restriction. The Office of Fair Trading is now looking into the matter and is quoted by the BBC:
"The OFT and the European Commission are aware of these issues and are currently in discussion about what action, if any, should be taken."
Olympic Medals won during the Beijing 2008 Olympics