Possible Clues:

• Hole for molten metal
• Amount of money initially paid for oil deposit
• Reservoir for oil
• A quantity of money and power? It could bring depression
• Waste reservoir
• When economy slows and pound drops it's a depression
• The Guardian turns on politician - there may be oil in it
• In business downturn, pounds down the drain
• Pit collecting water/oil
• Pit for collecting oil