Possible Clues:

• Type of gas
• Marsh gas — the name (anag)
• The name's been changed — it's a gas
• Greenhouse gas
• He meant to change to gas
• Complaint over old aristocrat? It derives from rotten matter
• Odourless, colourless, inflammable gas
• Name the original source of fuel
• Do be taken off drug when gas is found
• Me? A noble old Scotsman and a fiery old gasbag