The National Crime Agency (NCA) said a 23-year-old Sudanese national was detained in Hayes, west London, and is being interviewed by officers.
He has been arrested on suspicion of assisting illegal immigration and entering the UK illegally.
The move comes as two other males from South Sudan and Sudan have been charged over the incident, but disputes about their ages and if they are youths has delayed court proceedings.
The pair said they are 15 and 16 years old, while initial age assessments by immigration officers and a social worker placed them in their early 20s.
Further in-depth assessments have been ordered by Folkestone Youth Court.
The NCA previously said it was working with Kent Police, immigration enforcement teams and Border Force to support the French-led investigation into the incident off the northern French coast on April 23.
A dinghy carrying more than 100 people set off from Wimereux at around 6am but got into difficulty.
Three men, a woman and a seven-year-old girl died.
Some 49 people were rescued but 58 others refused to leave the boat and continued their journey towards the UK, the French coastguard said, with several other boats later embarking on the crossing.
The NCA said more than 50 people who were on board the dinghy which arrived in the UK have now been interviewed.
An 18-year-old man from Sudan has also been arrested over the incident and continues to be bailed pending further inquiries.
