Halve the potatoes and cook in lightly salted boiling water until tender. Rinse under cold water and leave to cool.
Meanwhile, slice the bacon into thin strips. Heat the oil in a frying pan and cook the bacon until golden; drain on kitchen paper and allow to cool. Finely slice the spring onions, reserving some for garnish.
Put the potatoes, finely sliced spring onions and bacon in a large salad bowl. Gently stir in the mayonnaise. Season to taste with salt and pepper, garnish with the reserved spring onions and serve.