Possible Clues:

• Like a robber all at sea with an H, by the sound of it
• H, as with Hook?
• When to knock off, roughly speaking?
• By way of a criminal to a pronounced extent
• Say hi to my favourite snake?
• At first Eliza didn't like bootleg version
• Breathe in; sound of h
• One of 17 across gets one angry to a criminal extent
• One cannot hear it when it is dropped
• Sound made by Hook initially, occupied thus?