"...but tried it and it was OK, though I haven't bothered since."

You must be doing it wrong. For a start, you need chip shop chips. They must be overloaded with salt 'n' vinegar. Take one slice of terrible white bread. Butter it thickly (when you bite into the butty your teeth should be leaving little cliff edges). Stork will do at a pinch. Load one half with chips then fold it over. Tommy K optional. Two basic rules should be followed: sit over your plate (or newspaper wrapping) to avoid buttery drips on the trousers, and make sure you've had five pints before you eat it. Viola!