Related Clues:

• Sour, or an open cake
• A bit sour like open cake
• A bit sour, like flattish pie
• Open pastry filled with apple or jam
• Pie with fruit filling
• Somewhat sour like flat cake
• Open cake with jam etc
• Tasting sour like a lemon
• Sour-tasting pie?
• Sharp or sour in taste
• Flat pie
• How a branch of the police, I see, gets biting
• However sweet, you'll not find her an 11 across
• If the biter turns up over the Wye it gives it a sharp smell
• A matter for the detectives, I see, but not for 31 across