The body was found by firefighters alongside a train platform in Coquelles, northern France. The force of the impact made it immediately impossible to identify the victim's sex, age or nationality.
Thousands of people from Africa and the Middle East fleeing war and poverty at home and lodged in makeshift camps in the French port of Calais are trying to enter Britain by jumping onto lorries or hiding on trains, disrupting cross-Channel freight and passenger traffic.
The influx has plunged the 28-nation European Union into crisis. Its leaders were discussing their responses at a summit in Brussels on Thursday and Friday.
(Reporting by Pierre Savary; writing by Michel Rose; Editing by Andrew Callus)