Possible Clues:

• It's plain: a road follower must turn round
• Treeless frozen Arctic plain
• Being so cold, it's up to the cockney to make it cracked
• Area of permanently frozen subsoil
• Vast level Arctic regions with frozen subsoil
• Region of permafrost
• Drive in fish to marshland
• Gets so frozen inside that it's hard for the cockney to crack up
• What's so fishy about the doctor to make him so cold? (6)
• Bleak prospect, one difficult to crack, heading off heavenwards