Cook the potatoes in a large saucepan of salted boiling water for 15–20 minutes until tender. Drain well, return to the pan and mash.
Heat a little oil in a frying pan, add the spring onions and cook for 2–3 minutes, then add the bacon and cook until browned. Add to the mash with the parsley. Season well with salt and pepper. Form the potato mixture into 8 cakes, then cover and chill in the refrigerator until firm.
Lightly coat the cakes in flour. Melt the butter in a nonstick frying pan, add the cakes, in batches, and cook over a medium heat for 4–5 minutes on each side until browned and heated through.
Meanwhile, to make the sauce, put the crème fraîche in a bowl and mix in the basil and tomatoes. Season well with salt and pepper.
Serve the cakes hot with the sauce.