The only designer that got involved in sport that immediately springs to mind is Stella McCartney with the Team GB 2012 gear and a few tennis collaborations with adidas.
After reading that information on the site it seems that you can buy two at the same time if you have the supporter numbers and are eligible.
Plenty of time yet, I'll just check if I'm eligible in a few days.
7430 in the queue
Only being able to buy one per person is a joke. How are you supposed to get two together?
Should definitely be able to get two if you have the supporter numbers to provide.