Good Will Riker wrote:
I will have to go back and rewatch Casino Royale on DVD to confirm this.
But, Le Chiffre's "Your friend Mathis is my friend Mathis" line as well as the suspicious powder inside the cup Mathis offers to James Bond is quite telling, eventhough M says otherwise at the end.
Le Chiffre said that so Bond would trust Vesper and not an actual ally. The powder is only suspicious because Bond doesn't trust Mathis at that point.