1: Loathing for leader leaving platform (5)
2: Record left by teacher in Siam (5)
3: Coats need woven yarns (9)
4: Crew member is one in operating room (3)
5: You audibly ram partner (3)
9: Biting piece of chocolate with dry exterior (5)
10: Proficient in arithmetic, starting with short division (5)
12: Unappealing environment for a snooze (3)