'Fraid I haven't seen that movie. Does he use this accent in Reign of Fire? (I haven't seen that either, but I recorded it from the TV and I'm planning to watch it eventually.)
David Mack said:
^ Pennington is described as being a Scotsman, so I think McGregor would have the accent he used in Trainspotting.
Given that McGregor isn't actually in Reign of Fire, it's extremely unlikely that he uses that or any accent in it.
His Scottish accent is best heard in Trainspotting, Shallow Grave, as one of his characters in The Island and in A Life Less Ordinary.