Belgian police are waving through migrants who are trying to travel to Britain illegally via sea ports in Belgium or northern France because they cannot be deported and cost £180 a day to hold in detention centres.

Under European Union rules the Belgian authorities cannot deport asylum seekers who have travelled through France to Belgium from Italy or Greece, which is usually where they entered Europe.

Areas of the Flemish west coast of Belgium have become a key route for migrants seeking to enter Britain via a Belgian sea port and local police forces have said that they are overwhelmed.

Wim Pieteraerens, the police chief for Kruibeke, a municipality in Antwerp, has instructed his officers not to stop illegal immigrants because it is “useless work”