Europol has identified more than 12,000 suspects in the illegal trade and says traffickers have set up operations in London.
Figures show that people-smuggling gangs, including those set up in London, netted nearly £5bn last year for trafficking migrants into Europe.
The UK is one of the three main targets for migrants, along with Germany and Sweden.
Migrant-smuggling networks into Europe now rake in more profit than arms sales and, in some countries, drugs.
Labelling people-smuggling as the “fastest growing criminal market in Europe”, the police report said: “This turnover is set to double or triple if the scale of the current migration crisis persists in the upcoming year.”
Europol and forces across Europe have identified more than 12,000 suspects in gangs involved in smuggling in migrants in the last year alone. They have a database of another 28,000 suspects.
EU border agency Frontex recorded more than 1.8 million illegal border crossings into the European Union in 2015.