Possible Clues:

• I wheel it out when a tactful comment is required
• Pardonable remark to rest on what bride's wearing
• Good fiction?
• "The dog ate my homework," e.g.
• Priest beginning to escape after festival — not such a wicked thing?
• Tactful deception
• We are prone to accept blow as pardonable offence
• It's not true to tactfully say 15 across might offer it as a wrong answer
• Just a pale fib
• Diplomatic deception