Possible Clues:

• Ascertain if one may set one's mind at rest
• Perhaps ascertain if one is silly enough to rue this
• Ascertain, perhaps, in a convincing way
• Allay one's fears
• Queen succeeded in America, backed by guarantee
• State confidently to
• State confidently
• Promise to take animal to water
• Cover with a policy
• Ascertain that this is like the start of 8 across to start with