A man wanted by French police is detained in Gloucestershire in connection with the drownings.
A man has been arrested over the deaths of at least 27 people who drowned attempting to cross the English Channel in a dinghy last year.
Harem Ahmed Abwbaker, 32, was arrested in Gloucestershire on Tuesday morning, the National Crime Agency (NCA) said.
He is accused of being part of a group which conspired to transport the migrants to the UK last November.
He is set to appear in court on Wednesday over extradition to France where he faces manslaughter charges.
The incident is thought to be one of the worst migrant tragedies in the Channel.
Mr Abwbaker, who will appear at Westminster Magistrates Court, also faces French charges of facilitating illegal immigration.
NCA deputy director Craig Turner described the arrest as “significant”.
He said: “The individual detained today is suspected of having played a key role in the manslaughter of those who died.
“Working closely with our French partners we are determined to do all we can to get justice for the families of those whose lives were lost, and disrupt and dismantle the cruel organised criminal networks involved in people smuggling.”