Related Clues:

• He might become quite a coxcomb with a car
• With an addition he might get relatively dirty
• He's under the car for the cock (5).
• He might go after the car for the comb
• He might make a comb after a car
• An addition would make him dirty
• That's relatively the last of 11 across
• An addition could make him relatively dirty
• It makes him boil to get under Car B
• Under the fur he would come to the boil
• He might have Car B on the boil
• If there were fur on him it would come to the boil
• One might comb him to a relative extent under the car
• Needs an addition to make him dirty
• He'll come to the boil under 21 down