The institute was founded on 2 May 1945, almost the moment the war in Europe ended. The timing matters. For Polish soldiers, airmen, sailors, and civilians scattered across the United Kingdom, victory came without homecoming. Under the Yalta Accords, one third of Poland's prewar territory had been ceded to the Soviet Union, and a communist government installed in Warsaw. The pilots who had fought in 303 Squadron during the Battle of Britain, the sailors who had hunted the Bismarck aboard the destroyer Piorun, the soldiers who had climbed Monte Cassino - many could not safely return. So they did the next best thing. They preserved what they had carried: witness testimonies from the Warsaw Uprising of 1944, regimental flags, medals, uniforms, the personal effects of statesmen and ordinary men and women. They built a memory of Poland in West London because the actual one had been taken away.

Władysław Sikorski was Poland's prime minister-in-exile and commander-in-chief of its armed forces in the West. He died in 1943 in a plane crash off Gibraltar, leaving the diaspora without its most prominent leader. Naming the institute after him was both tribute and statement: this was Sikorski's Poland, the one that had fought on through 1939, 1940, 1944, the Poland that would not be remade in Moscow's image. The walls hold a turret from a 7TP light tank used against the German invasion in September 1939 - later captured, used by the Germans in France, then recovered during the Allied advance of 1944 - a single artifact tracing the long arc of the war. Nearby, a memorial honors the thousands of Polish men, women, and children deported east and starved on Soviet soil.

In 1948, veterans led by General Tadeusz Bór-Komorowski - the man who had commanded the Warsaw Uprising - founded the Polish Underground Movement Study Trust, the Studium. For forty years it operated separately, gathering documents about the Polish Underground State, the largest clandestine resistance organization in occupied Europe. In communist Poland, this history was banned or censored. In Ealing, it was preserved. The two organizations merged in 1988, the year the Polish communist system began to collapse, as if the archive had outlasted the regime it documented. The Studium kept its internal autonomy, continuing its research from its Ealing base.

The building itself has a quiet irony. The Victorian terrace was built by Charles James Freake, the same developer who built the nearby Polish Hearth Club. Kensington Road faces Hyde Park - parade ground of empire, where coronations and jubilees have rolled past for two centuries. A few minutes' walk away sit the Royal Geographical Society, the Albert Memorial, the Albert Hall. The Polish Institute sits among these monuments to British grandeur, holding the story of a country Britain went to war to defend in 1939 and then, six years later, agreed at Yalta to leave on the Soviet side of the line. The institute's chairmen have included Count Edward Raczyński, Polish ambassador to the Court of St James's from 1932 to 1941, who lived to be a hundred and watched Poland become free again before he died.

Among the most visited exhibits is a bronze sculpture by David Harding of Wojtek - the Syrian brown bear adopted as a cub by Polish soldiers in Iran in 1942, who travelled with the 22nd Artillery Supply Company through Iraq, Egypt, and Italy, who carried artillery shells at Monte Cassino, and who lived out his retirement in Edinburgh Zoo. He was officially enlisted as a private to allow him passage on troop ships. The institute's collection has this kind of texture: a hussar helmet from the 17th century, a manuscript by the national poet Adam Mickiewicz, a bust of Jan Sobieski, the emblem of the 1st Polish Armoured Division. Over five thousand photographs were digitized by the Karta Center in 2005-6 and sent back to Poland for exhibitions and education. The objects went home even when the people could not.