Possible Clues:

• Attempt to keep one pound in hat
• Impressionable singer in hat Sinatra wore?
• Attempt to obtain one pound hat
• Felt hat with an indented crown
• Quivering sound curtailed by singer in novel
• Leaves from livery stable with O'Ferrall's novel headgear
• Narrow brimmed hat often seen at horse races
• One pound in tax? It'll go over your head
• Strain to acquire one pound for headwear
• Hat named after the eponymous heroine of a George du Maurier novel of 1894