Read this story in the '70s but it might have published earlier. Certain it was by a British author. Tells two stories - one in WW2 Burma and one in the present. An RAF plane is shot down over Burma - the two men bail out and land in two different villages. British troops reach one village and reward the villages for helping their man. The present: an alien spacecraft - a warship - crashes on Earth and Earth people help the wounded pilot. Burma WW2: the Japanese reach the second village and massacre the inhabitants for helping the British.
As confirmed by the original poster in the comments, this is "Even chance" a short story by John Brunner, first published in Analog Science Fiction / Science Fact in November 1965. It can be read online here.
It begins in World War 2, when a photo-reconnaissance plane is shot down over the inaccessible northern hills of Burma, and the pilot and the navigator bail out. The pilot lands among the Kalangs, and is well-treated, due to his impressive way of arriving “on white wings from the sky”. A (presumably) British search party richly rewards the natives, and the chief orders anyone who arrives floating from the sky should be treated similarly. At the end of the story this is contrasted with the fate of the navigator. He too received a friendly welcome from the natives who found him, the Ipoh, but when a Japanese search party found him “the officer in charge very properly razed the village to the ground and shot the chief for collaborating with the enemy”.
A generation later a meteor is seen in the sky. The son of the chief, Tambah, finds the wreckage of a crashed vehicle, but instead of showing it to the tribal elders he carries a chunk of metal from it out of the jungle to gain respect from his peers and maybe obtain a reward. Along the way he gets sick but keeps going until he makes contact with a WHO vaccination team. They find that the boy's sickness is due to the piece of metal being highly radioactive, and deduce that the vehicle must have been a nuclear-powered rocket. The authorities in Rangoon start an aerial search for the crash site and eventually find the wreckage with the pilot within it, the pilot being an alien. Examining the wreckage revealed that the craft was not actually nuclear powered, but had been hit by a nuclear weapon, shot down by hostile alien forces. The story ends with the loaded question “Who’s going to come looking for the survivors?”. Will the Earth have the fate of the Kalangs or of the Ipoh, the "even chance" of the story's title.