Possible Clues:

• 'Yarn of Two Cities', taking only half second
• The North gets what's only all synthetic
• Being synthetic, it's made of only Nitrogen
• Product first used commercially in toothbrush bristles
• Comedian ultimately requires only funny material
• Material carried by many Londoners
• Many long stockings contain this
• The North can only produce this synthetically
• Material essential for many Londoners
• Material many longshoremen pick up