Five men have been arrested after migrants were found hidden in a cattle truck.
The swoop was part of National Crime Agency investigation into a crime group suspected of hiding the migrants to smuggle them into the UK.
A total 13 people, including a child, were found in a hay compartment of the lorry carrying livestock in the port of Calais on Saturday evening.
Border Force officers had searched the vehicle acting on information from the NCA.
After that the British lorry driver, was detained by the French authorities.
Four more men, aged between 23 and 39, were then arrested by the NCA on suspicion of facilitating immigration.
This was done in a series of raids in Romford, north-east London, and Brentwood, Essex.
NCA investigators also searched properties in Grays, Essex, and Worthing, West Sussex.
At one a substantial amount of cash, thought to be around £100,000, was seized.
The four men arrested by the NCA were questioned and later released under investigation. The man detained in France remains in custody.
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.
"They do it 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.”
This is the latest in a long series of suspected illegal immigration incidents.
On Sunday 13 migrants were picked up in the Channel in an inflatable boat by the Border Force.
Other incidents over the last year have happened in the coastal areas of Dover, Deal, Folkestone and Romney Marsh.