I posted this last year but I think it bears repeating here. Craig and Arlene are used to working with accomplished professionals for the purpose of putting on a show for a paying public (So you had better be pretty darn good, or you're out). Len is used to working with those just starting out in dancing (whether for fun or the beginning of professional career), and so I suppose is more inclined to encourage those less gifted.
HOWEVER never (or often interrupting) letting Arlene finish a sentence is just plain rude. Never using the full range of marking to reflect how good or bad a dance is, as well as overmarking simply to "spite" Arlene and Craig distorts the leaderboard. Finally it strikes me that if SCD were to end tomorrow Craig and Arlene would go back to being highly respected West End chereographers, whilst Len would go back to teaching kids at his dancing school (not a criticism folks, merely an observation). And I always felt that Len got the job probably because he's one of Brucie's golfing mates (not that I know that for a fact or anything)