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Seven men were arrested on suspicion of entering the UK illegally on Tuesday at the Port of Dover's Eastern Docks.
A group - made up of three Iraqi nationals aged between 22 and 27, and four Iranians between 21 and 25 - were found on-board Calais Seaways, a DFDS vessel.
It caused delays of up to 60 minutes for passengers waiting to cross the English Channel.
All of the men remain in immigration detention, according to the Home Office.
Two minors were also found at the scene and have been passed to the care of Kent Social Services.
A Home Office spokesman said: "Where someone is found to have no right to remain in the UK, we will take action to remove them."