France is threatening to arrest British activists trying to stop migrants leaving French beaches on small boats bound for England. Sources close to Laurent Nunez, the French interior minister, said he wanted to see the Britons arrested for possible obstruction and aggravated violence. It follows a series of vigilante-style actions by Britons from the Raise the Colours movement, which encourages the widespread public display of flags bearing the Union Flag and St George’s Cross. Raise the Colours activists have published videos online of what they describe as “civilian border control” or “Operation Stop the Boats”. The films show them wading...