ESSEX‚ England—Wethersfield is a postcard village about 50 miles from London. A row of well-kept houses on a country lane leads to a tiny village green, a little school, and St Mary Magdalene, the 13th-century parish church. In a field just north of the village on a recent afternoon, a young Middle Eastern-looking man sat against a hedge, texting on his cell phone. I walked toward him and said hello. But when he saw me, he seemed frightened. He scrambled to his feet and stumbled diagonally across the muddy furrows, running for the tree line.

The British government is using the old air base at Wethersfield as a camp for asylum seekers. It’s unclear when they came to the UK, as the government does not release information on how long their processing takes. But we do know this: All are adult men. Many crossed the English Channel from France, arriving on small boats and claiming asylum when they hit the beach. They are from countries such as Afghanistan, Eritrea, Iran, Iraq, and Syria. They are allowed to come and go freely from the camp, to the village and beyond.

Currently, 580 of them live on the base. Their number is about to rise to 800. The government won’t say exactly when, but it had initially stated that a total of 1,700 migrants would eventually move here.

Before the migrants arrived, the village of Wethersfield reportedly had a population of 707.

Originally the site of the camp was earmarked for a new prison, a proposal which aroused local opposition. When the government first reopened it as an asylum center, the locals were told it would be temporary, but no one believed that...