It just looked to me like he was going slow and the others were letting him until Cobden moved to within a length or so. Even then, the others seemed very content to lay off him, and they looked still on the bridle. To me, that allowed his basic speed to kick in over the last six furlongs and they couldn't get near him.
Id say that's completely wrong. Horses like Minella Indo, Janidil and Galvin were under pressure a mile from home. Others were going as quick as they could - without any guns being put to their heads 1.5m from home. Clan was actively out there to pressurise and both Allaho and Clan finished very slowly. As Townend said "I didnt dare look around me after the last"....there was nothing left.