If you're watching your fat levels, try switching mayonnaise and crème fraîche for natural yougurt. Add a pinch of sugar or a drop of honey to counteract the sharper flavour.
Boil potatoes for 15 mins or until tender. Drain and cool under cold water. Meanwhile, make the dressing by mashing anchovies with the mayonnaise. Add the white wine vinegar or lemon juice and season to taste with black pepper. Tear the leaves from the lettuce into a large bowl. Chop spring onions and tip them in. Slice the potatoes and add to the bowl, then
drain the tuna and flake into the bowl. Drizzle the dressing over and serve.