Four men were arrested in a series of raids in Romford and Brentwood as part of an investigation into a crime group suspected of hiding migrants in a cattle truck.
The arrests followed the discovery of 13 migrants including one child found in a hay compartment on a lorry carrying livestock in the port of Calais on Saturday, October 19.
After the lorry was searched, a British national was detained by the French authorities.
Four men aged between 23 and 39 were arrested by the National Crime Agency (NCA) on suspicion of facilitating immigration following a raids in Romford and Brentwood.
NCA regional head of investigation Gerry McLean said: "Those who seek to profit from facilitating illegal immigration into the United Kingdom do so for their own selfish greed and without any concern for the health and wellbeing of those who are often moved across borders in inhuman and degrading conditions.
"We are determined to do all we can with our law enforcement partners to disrupt those networks and bring perpetrators to justice.
"Our investigation into this incident continues."
The four men have been released under investigation and the man detained in France remains in custody.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here