I'm a Brit living in Canada and I concur, in general the British are terrible at sandwiches. However, I would say that outside of Subway and arguably Mr. Sub, North Americans aren't a whole world better at making them.

I'm a firm believer that if you ain't putting any love into making the sandwich, it's not worth eating. The only exception where you need simple is butter and salt and vinegar crisps. Everything else requires lettuce, tomato and cucumber, salt and pepper and depending on the meat a proper condiment for that meat - Ham & Mustard; Turkey & Cranberry Sauce; Chicken & Mayonnaise; Beef & Horseradish Sauce.