The suspects are accused of trafficking up to 10,000 people across the English Channel in small boats in the last year.
European police forces say they have separately conducted "the largest international operation" against an organised crime group between France and the UK.
Authorities in five European countries detained 39 people in a major cross-border operation targeting an Iraqi-Kurdish gang, Europol said.
The suspects are accused of trafficking up to 10,000 people across the English Channel in small boats in the last 18 months, making around €15 million.
Britain’s National Crime Agency said six people were arrested in the Docklands and Catford areas of London. Dozens of raids also took place in Germany, France and the Netherlands.
Police in the German city of Osnabrück said 18 people were arrested in northwestern and southwestern Germany on suspicion of involvement after more than 900 police officers carried out 36 searches.
Nine more suspects were detained in France, and six others in the Netherlands.
Police also seized more than 1,200 life-jackets, 150 rubber boats and around 50 engines as well as tens of thousands of euros in cash, weapons and drugs, Europol said in a statement.
More than 28,000 migrants crossed the Channel to the UK last year, compared to just 8,500 in 2020.
Dozens have died while attempting the crossing, including 27 people from a packed boat that capsized in November.
'Victims of labour exploitation and domestic slavery'
Meanwhile, in a separate operation, Europol said that had arrested over 130 other suspected migrant smugglers.
Europol said in a statement that law enforcement officials identified "around 130 potential victims" -- including more than 10 children -- in the operation.
"Many fall victim to sexual exploitation, forced begging or different types of forced criminality, including petty crimes and drug trafficking. They also become victims of labour exploitation and domestic slavery."
"More than 22,480 law enforcement officers took part in the [joint] action days, during which checks were carried out at European sea, land, and air borders, with an additional focus on heavily utilised routes into Europe," Europol added.
Authorities in 22 different European countries were involved in the "days of action" in June, as well as Frontex and Interpol.
This article has been updated to reflect the separate police operations in migrant smuggling.