Many countries have a famous defeat or last stand. Dunkirk is ours; our Thermopylae, our Alamo, our Stalingrad, our Pearl Harbour. Many countries also have a famous mobilisation of the people - a revolution, something with a national day to name streets after. Dunkirk is ours.
The popular memory of Dunkirk is one of spontaneous organisation. Not an organised event run by the state, but one where the official efforts had already failed and British lives could only be saved by a mass ad-hoc action by whichever members of the public happened to be at hand to crew a boat. This ties in with the wider popular memory of the war as "total effort": everyone was a contributor.
This leads to "Dunkirk spirit": spontaneous solidarity in the face of adversity. Often invoked lightheartedly in the face of ordinary disasters like being stuck on a train for hours or squelching about a drenched music festival, but it works for more serious events too. It was invoked a lot when the Ariana Grande concert was bombed in Manchester. This is part of why there is no real counter-part to the individualism of survivalists or "preppers" in the UK: everyone believes that when a real disaster happens, you can rely on your fellow members of the public, and we will survive together.
A detail of the news interview that is very relevant to the whole thing is "stiff upper lip", and responding to threats with blithe dismissal and flippancy. The officer on the beach saying "I wish they wouldn't do that" about the strafing is the exemplar here. But there's quite a few famous, extreme examples: https://www.warhistoryonline.com/featured/major-digby-tatham...