Towards the end of T2: Trainspotting, we are informed that the huge grant (100k) had been stolen by Veronica, as she made Spud forge Simon and Mark's signature. Spud got his share (which he deferred to his estranged family).
My question is, why would Spud do that? I mean, Mark saved his life (on top of never ripping him off in the first place). We aren't informed of any problems between Simon and Spud.
Spud would have gotten a share anyway... And he knows it's a bad thing... He later tells that to his "friends" (He later saves their lives, which I guess evens the score).