Walker: "I nearly bought a wool jumper in town. £140. Nice work if you can get it." Farmer: "I got about £2 for the fleece." Walker: "£2?" Farmer: "Per sheep, per year. Clipped it off her in two minutes, rolled it, bagged it, drove it to the depot. The cheque for the whole flock didn't cover the diesel." Walker: "Then who's getting the £140?" Farmer: "Not me, not the shearer. He costs me more per sheep than the wool fetches. I pay to have it taken off." Walker: "So you lose money shearing." Farmer: "Every year. And I can't not shear, or she cooks in July and the flies eat her alive. The wool's a welfare job that used to be an income." Walker: "Sell it yourself, then. Cut out the middleman." Farmer: "Not allowed. By law it goes through the board. Has done since 1950. I can keep a fleece for the wife to knit with, and that's about the extent of my freedom." Walker: "So where does it go?" Farmer: "Washed in Bradford, if we're lucky. Shipped to China, spun, knitted, shipped back, and sold to you with a label about heritage. By the time it's in the window there are eleven people between us and I'm the only one who met the sheep." Walker: "That's mad." Farmer: "My grandfather paid the rent on the wool cheque. I pay a man to take it away. Same sheep, same hill, same jumper in the window. Only the price of the farmer went down." Walker: "What would fix it?" Farmer: "You buying the jumper. And asking them where the other £138 went."

The lowest point of land in Britain is a cast-iron post in a Cambridgeshire wood, and when it went in the ground it was level with the ground. Stand next to it now and it is four metres over your head. It is at Holme Fen, south of Peterborough, and in 1851 this was the edge of Whittlesey Mere, the largest lake in southern England. A syndicate of landowners drained the lake that year for farmland, and the engineer, who knew what happens to peat when you take the water out of it, drove an oak pile through 22 feet of it down to the clay and cut the top flush with the turf. A column from the Crystal Palace replaced it. Then they stood back and watched the land go down. Nine inches in the first year. Eight feet by the 1890s. Today the ground around that post is 2.75 metres below sea level, and the post is a ruler nobody asked for, sticking out of a birch wood with guy ropes holding it up because the soil that used to hold it up has gone into the sky. That is what drained peat does. It dries, it shrinks, and it oxidises, which means it turns into carbon dioxide and leaves. Peat takes a thousand years to lay down a metre. Under the plough it loses a centimetre or two of that every year, and the Fens have been under the plough since the Dutch engineers arrived in the 1600s. Peat soils farmed for crops are among the largest sources of carbon dioxide in Britain's whole land sector, and the fields doing it are growing lettuce. Because that is what the Fens are for. A third of England's vegetables come out of this one flat black square: half the lettuce grown in Britain, three quarters of the celery, the carrots, the onions, the potatoes, the leeks, the beetroot. The bag of salad, the celery sticks, the chips. Every field of it is a few millimetres lower than it was last January, the pumps run day and night to keep the sea out of a landscape that is now beneath it, and the water the crops need is forecast to run short within ten years. Before the drain this was eels, wildfowl, reeds, summer grazing, and a fen that had been quietly stacking carbon since the ice left. The cattle came and went on it for 5,000 years and the ground stayed where it was. The salad has been on it for 170 years and the ground is four metres down. The post is still measuring.