Heat 1 tbsp oil in a frying pan, then add the leeks and cook until softened. Tip the cooked leeks into a bowl with 100g breadcrumbs, the cheddar, chives and 2 eggs. Mix together well, then place the bowl in the freezer for 5 minutes.
Place the remaining breadcrumbs in a shallow dish. Put the remaining egg into another shallow dish and gently beat.
Take the mixture out of the freezer and shape into 6 large sausage shapes or 12 smaller ones. Dip each sausage in the egg, then roll in the breadcrumbs.
Heat the remaining oil in a frying pan and, over a medium heat, fry the sausages for 10 minutes until golden and cooked through.