Poland has often been the victim of great-power politics. In its hours of need it has looked to Britain, and has offered support in turn. That relationship is epitomised in events 70 years ago today. On 1 September 1939, the forces of Nazi Germany crossed the border into Poland.

The aggression demonstrated the futility of the British Government’s attempts over the previous decade to avoid war by concession and negotiation. A commitment to Polish independence drew Great Britain into a war that was catastrophic, but just and necessary. It was one of the ironies of history that the guarantee to Poland had been extended by Neville Chamberlain (who thought it “unprovocative” to Germany).

An ailing and politically quiescent Prime Minister, who had been outmanoeuvred on the international stage, belatedly did the right thing nonetheless. For the next six years Britain’s fate was integral to Poland’s prospects. London became the headquarters of Poland’s government-in-exile; Poles fought alongside British troops to preserve Western civilisation from barbarism.

Even in the heyday of Victorian Liberalism, British support for the independence of Poland had been strong but mainly rhetorical. Viscount Palmerston voiced support for Polish rebels seeking independence from Russian domination in 1863. But with Bismarck supporting Russia, that was the diplomatic limit. The closeness of the Anglo-Polish connection was forged in the 20th-century battles against tyranny.

Poles demonstrated fortitude as their country was occupied in the last century by succeeding forms of totalitarianism. Nazism was repelled, but Poland became the initial cause of the breakdown of the wartime alliance of Britain, the US and the Soviet Union. At the Yalta conference of the Big Three powers, Stalin promised elections in Poland that he had no intention of allowing. The Soviet Union installed a communist regime in Warsaw. Yalta was seen widely by Poles as a betrayal, and Winston Churchill stated his concern at Russia’s designs on the Polish frontier. But there was little in practice that could be done by the US and Great Britain, short of war.

Tied to the Soviet Union through the Warsaw Pact and economically decrepit, the communist regime proved unable to satisfy the pent-up demands exemplified in the riots of 1956, known as the Polish October. Poland proved utterly infertile ground for an indigenous communist movement. Communism remained in power because of Soviet demands rather than popular preferences. And especially after the glimmerings of freedom in Czechoslovakia in 1968, it required repression and purges to maintain its authority.

Britain, meanwhile, provided a home for a burgeoning exile community of 70,000 Poles who had remained after the Second World War. It gave support too to the emerging Solidarity movement. When Margaret Thatcher visited Warsaw in 1988, she and Lech Walesa were decorously mobbed by the congregation of the Church of St Brygida. In its journey from communism, Poland has taken a circuitous ideological journey, encompassing the right-wing populism of the twins Lech and Jaroslaw Kaczynski. But its status as an integral part of a tolerant, liberal continent is unquestionable. As Tony Blair said on its accession to the EU in 2003, Poland is, for Britain, an old friend in a new Europe.