The field takes its name from the Sole Pit, a deep underwater basin in the southern North Sea named for the sole fish that trawlers once dragged from it in quantity. Geologists liked the name and applied it upward, to a gas-bearing structure they identified in the rock beneath the Pit: West Sole. The structure runs northwest to southeast, about 12 miles long and 3 miles wide, sitting entirely within UK Block 48/6. Below 9,000 feet of seawater and sediment lies the Rotliegendes sandstone of Lower Permian age, a layer between 80 and 131 metres thick - the same red bed that contains most of the southern North Sea's gas. Sealed above it is the Zechstein salt, a wall of crystallised seawater laid down when the Permian sea evaporated, which kept the gas from leaking upward for 260 million years.

BP, which developed West Sole, named its later platforms in the area for villages that no longer exist. Cleeton, Dimlington, Hoton, Hyde, Newsham, Ravenspurn - all once stood on the Holderness coast of East Yorkshire and all have been swallowed by the North Sea over the centuries. The Holderness coast erodes faster than almost any shoreline in Europe, losing roughly two metres a year to the sea. Whole medieval villages have gone under. Naming gas platforms after them was a kind of memorial in steel, applied by engineers who probably didn't think of it as poetry. The Cleeton platform is still out there. The actual Cleeton was lost about 700 years ago.

The original estimate put the gas in place at 57 billion cubic metres - enough to heat several million British homes for years on end. Production climbed through the late 1970s and peaked in 1983 at 1,719 mcm in a single year. After that came the long, gradual decline that every field eventually faces: 1,500 mcm through the mid-1990s, around 1,000 mcm into the early 2000s, then dropping below 500 by 2014. The gas is leaving. The reservoir is depleting. The platforms continue to operate at reduced capacity, with adjacent fields tied back to share infrastructure. Britain's gas demand long ago outstripped what the North Sea can supply, and most of West Sole's output now blends into a much larger import-dependent system.

The two pipelines from West Sole - 16-inch and 24-inch in diameter - come ashore at the Easington gas terminal on the East Yorkshire coast, where they join one of the largest gas-receiving complexes in Britain. Easington is where North Sea gas becomes British gas; where it is metered, conditioned, blended with imports from Norway and Qatar, and pushed into the National Transmission System. The terminal sits on a low coast prone to the same erosion that took Cleeton, defended by sea walls and constant vigilance. The original West Sole gas first reached Easington in March 1967 - a moment that historians of British energy mark as the start of the gas revolution. Within seven years, every gas appliance in the country had been converted.

West Sole is still producing. That alone makes it remarkable - most contemporary fields are decommissioned. The platforms have been through multiple rebuilds, ownership changes, and process upgrades, but the wells in 9,000 feet of Permian sandstone still flow. Stand on the Holderness cliffs at dusk and look east, and on a clear night you can sometimes see the gas-flare glow from the fields offshore. The flares are smaller now than they were - flaring is discouraged, gas is too valuable to burn - but the platforms keep their navigation lights bright. They are a working memorial to a moment when Britain looked at the North Sea and saw not fish or trade but a vast underground reservoir of warmth, ready to be tapped.