Irregular migration to the UK "is increasing", an anti-trafficking expert said.
Andy Desmond, Director of Anti-Trafficking Consultants, told Good Morning Britain that the hot weather simply makes cases, such as those of migrants in lorries, "more overt because of their own distress."
Following the discovery of 35 Afghan Sikhs in a shipping container at Tilbury Docks at the weekend, a lorry has been discovered carrying 15 migrants with suspected dehydration in Somerset. The German driver has been arrested.
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Thursday could be the warmest day of 2017 so far, with temperatures of 22C (72F) forecast, double the average for March.
Former cricketer Andrew Flintoff and Tony Blair's ex-spin doctor Alastair Campbell talk about mental health battles in a series of films.
Row over apparent threat to security co-operation with the EU unless it agrees to a trade deal is a "misunderstanding", a minister has said.