The carve-up was decided in February 1945 at a Crimean resort while German cities still burned. Churchill, Roosevelt and Stalin met at Yalta and agreed that Germany would be sliced into four zones - British, American, Soviet, and a French sector to be cut from the Anglo-American share. The August Potsdam Conference made it official. Britain drew the short straw and the long one at once: the smallest landmass after France, but the heaviest population, the deepest war damage, and the industrial heart of Germany. The British zone stretched from the North Sea coast through Lower Saxony to North Rhine-Westphalia. Within its borders lay the Ruhr coalfields, the synthetic-oil refineries, the U-boat pens at Kiel, and the bombed-out warehouses of Hamburg. To form the French zone, the British ceded the Saarland, the Palatinate, and the Rhineland as far south as Remagen. The Inner German Border - the future fault line of the Cold War - was drawn on the same maps.

By December 1945, some 800,000 men of the British Army of the Rhine were billeted across the zone, and many German cities offered them no roof. Hamburg had been incinerated. Cologne, just over the line in the American zone, lay in pieces. Field Marshal Bernard Montgomery was named military governor on 22 May 1945; the British headquarters settled at Bad Oeynhausen. The German population that winter was being kept alive on rations that would not, in the long term, keep anyone alive. Hamburgers received about 1,340 calories a day; in the Ruhr, where the work was hardest, miners and their families lived on 840. To prevent mass starvation, Lord President Herbert Morrison cut a deal with the Americans: 675,000 long tons of grain would cross the Atlantic to Germany, in exchange for Britain accepting 200,000 fewer tons for its own already-rationed people. Britain was feeding its former enemy with bread it could not spare.

Under Ordinance No. 46, the Control Commission for Germany - British Element redrew the political map of north-west Germany. Three new states emerged from the wreckage. Schleswig-Holstein took its modern shape in 1946 out of the old Prussian province. Lower Saxony was assembled in the same year by gluing together Brunswick, Oldenburg, Schaumburg-Lippe and the former kingdom of Hanover. North Rhine-Westphalia, eventually Germany's most populous state, was stitched together between 1946 and 1947 from Lippe, the Rhineland's northern reaches, and Westphalia. The free city of Hamburg was restored as a German state - though kept inside the borders the Nazis had drawn for it in 1937. Bremen and Bremerhaven, isolated inside the British zone, became an American exclave so that the landlocked U.S. sector could reach the sea. These were not just administrative lines; they remain the federal architecture of Germany today.

British war-crimes investigators worked fast and publicly. The Belsen trial opened in autumn 1945, less than six months after British troops walked into the Bergen-Belsen concentration camp and found the dead stacked in pits. Forty-five former SS men, women and kapos stood in the dock; eleven were hanged on 13 December 1945, including the commandant Josef Kramer and the guard Irma Grese. The executions at Hamelin prison were carried out by Albert Pierrepoint, who between December 1948 and October 1949 hanged 226 people for British military courts - sometimes more than ten in a day. The Hamburg Ravensbrück trials ran for two years at the Curio-Haus in the Rotherbaum quarter. By 1948 the appetite for prosecution had cooled; Soviet pressure was rising, and the British government had decided that rebuilding the German economy mattered more than punishing the last unrepentant Nazis. The War Crimes Investigation Teams had handled around 350 cases involving more than a thousand defendants. Then the files closed.

Out in the North Sea, the British inherited Heligoland - a fortified rock that had hidden U-boats and bombed Britain. On 18 April 1947, the Royal Navy detonated 6,700 tonnes of leftover German munitions on the island in a single blast. Sailors called it Operation Big Bang. It was one of the largest non-nuclear explosions ever set off, audible across the German Bight, and it permanently rearranged Heligoland's geology. A new feature, the Mittelland, appeared where solid sandstone had been. Inland, British scientists were busy with quieter operations: Operation Backfire launched captured V-2 rockets from a pad near Cuxhaven in October 1945, fired by German technicians on loan from the Americans, one reaching 80 kilometres above the North Sea. Operation Surgeon spirited 1,500 German aerospace specialists west to deny the Soviets their skills. On 21 September 1949, the British zone formally dissolved into the new Federal Republic of Germany. The military governors went home. The barracks did not - some would stay British for another six decades.