Possible Clues:

• The way to beg in at the 2 down?
• Rousing undercover operation traps Jack
• At first, looking hard around for a little tea
• A sailing man in some irritation getting under way
• Celebrity can ultimately flag, showing sudden alarm
• Beginning to grasp the knack: smart
• To beg in this would not be the last thing you'd be doing
• Beginning to sing sharp in it
• Tell about pastry that's going off
• Rousing carol with bitter content