LONDON — The immigration authorities in Britain, Belgium and France carried out coordinated raids at scores of addresses on Wednesday to round up people suspected of being members of gangs that smuggle people across or under the English Channel as stowaways in long-haul trucks.

The raids by 150 law enforcement officials in Britain alone represented “one of the biggest operations of its kind ever undertaken,” said Chris Foster, a senior investigator with the United Kingdom Border Agency.

People-smuggling offers organized gangs potentially rich pickings as desperate migrants from troubled lands including Iraq, Iran and Afghanistan pay up to $10,000 each to be spirited past Britain’s strict border controls and across physical barriers, particularly the English Channel.

Trucks cross the channel by ferry or through a tunnel leading from Calais in France to near Folkestone in England. Such is the desire to cross the channel that migrants, some of them children, face huge hardships.