Possible Clues:

• Reveal a secret to hand over monopoly?
• What kind shooters do on Glorious Twelfth, snitch?
• Take a bribe to reveal a secret
• Almost assumed most of them in 10 across and 24 across let the cat out of the bag
• Spoil a surprise
• Divulge present draughts
• Concede one must have let the cat out of the bag?
• Reveal a secret present and the match is off
• Let slip drop vital catch, perhaps?
• Let cat out of bag - dispose of bag for nothing