The UK's borders used to be hilariously lax. In 2000 I travelled a lot. To leave, as you note, you just left.
To return, you'd walk past a man at Heathrow who was invariably reading the paper. He had his feet up on the desk. You were walking at a clip, passport held aloft, photo page ostensibly open towards him.
To return, you'd walk past a man at Heathrow who was invariably reading the paper. He had his feet up on the desk. You were walking at a clip, passport held aloft, photo page ostensibly open towards him.
That was it. Immigrated.