Preheat the grill to hot. Line a baking tray with foil and grill the bacon until crisp and golden.
Meanwhile, sift the flour into a bowl and season. Make a well in the centre and add the egg. Whisk in enough milk to make a smooth, thick batter. (This will make 12 pancakes.) Stir in the spring onions and mustard.
Heat the large non-stick frying pan and drop in evenly spaced spoonfuls of the batter. Cook for about 2 minutes until bubbles form on the surface, then turn and cook for another 1-2 minutes. Repeat with the remaining mixture.
Pile 3 pancakes onto each plate and serve with the crispy bacon and maple syrup. Freeze the remaining pancakes to use another time.