Landis provided the positive sample after a brilliant ride in the 17th stage, a gruelling ride to Morzine in the French Alps, a day after a disastrous showing had appeared to ruin his chances of victory.

The American said that the night before the 17th stage he and his Phonak team mates had been depressed and had drunk beer and whiskey in their hotel room.

When asked to explain his incredible ride in the crucial 17th stage, Landis replied: "There's 20 stages in the Tour and everyday you see a fabulous performance. Explain the other 19."