It’s 4:30 a.m. in Stratford, East London. The streets are quiet, the air crisp, and the sound of suitcase wheels tapping against the pavement echoes faintly. In a cosy terrace house, a group of six friends are gathering—still half-asleep but buzzing with excitement. Their flight to Spain leaves in three hours, and instead of juggling taxis or dragging bags on the Underground,...