A Romanian man has been arrested on suspicion of assisting unlawful immigration, a Border Force spokesman said.
He added that eight Afghani nationals have also been detained and a criminal investigation has been launched by immigration enforcement officers.
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Clear and cooler conditions to the south and east with lows into single figures.
Police have arrested three teenagers and a man following the shooting of a three-year-old girl with an air gun.
Police have released new images of the site of the fatal crash near Shoreham Airshow in which at least 11 people died.