A family of seven was found near the Kent coastline on Sunday after an empty dinghy was spotted in the Channel.
The Home Office said the mother, father and five children had been transferred to immigration officials for interview.
Border Force officials were alerted at 4.20am after the dinghy was spotted off the coast at Kingsdown.
Border Force are confident the vessel was used for a migrant crossing Home Office
It was later recovered a mile off shore.
The Home Office spokesman said: “Border Force are confident the vessel was used for a migrant crossing.
“Since the Home Secretary declared a major incident in December we have tripled the number of cutters operating in the Channel, agreed a joint action plan with France and increased activity out of the Joint Coordination and Information Centre in Calais.”
The Home Office added that the number of people attempting to cross the Channel went down from roughly 250 in December to 90 in January, with about half of the January attempts being intercepted in France before reaching British waters.