A Sudanese man has been arrested on suspicion of endangering life after four migrants drowned trying to cross the Channel.
Two men and two women died as they attempted to climb on to a dinghy at Equihen-Plage, near Boulogne-sur-mer, on Thursday morning.
The National Crime Agency (NCA) said the 27-year-old was arrested at the Manston processing centre in Kent.
Thirty-eight people were returned to the French shore after the incident south of Boulogne-sur-Mer near Calais, but 74 migrants travelled on to the UK.
The arrested man remains in police custody. The NCA is also in the process of interviewing those who made it to the UK.
Two children were among those taken to hospital as a precaution after the incident and another person was treated for hypothermia.
The NCA is helping French authorities with their investigation.
Government official Francois-Xavier Lauch, the prefect of Pas-de-Calais, told reporters the people who died were “already quite far into the sea”, adding: “The currents, which can be dangerous here, swept them away.”
It came a day after French emergency services took part in a training exercise to practise dealing with migrants in the water at the same beach where the deaths happened.
Last week, two migrants died in a similar crossing attempt – thought to be the first so far this year.
Craig Turner, NCA deputy director, said: “Working with colleagues at home and abroad, we are determined to do all we can to identify and bring to justice those responsible for these four tragic deaths.”
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