Heat the oil in the frying pan and fry the sausages gently for 10 minutes, turning every now and and then until nicely browned all over. Transfer to a the saucepan or casserole dish and set aside.
Fry onions over a medium heat for 5 minutes till they start to soften, stirring often. Add garlic and cook for 2-3 minutes until onions turn pale and golden brown.
Sprinkle the chilli powder and cook together for a few seconds longer. Then stir in the tomatoes, stock, tomato puree, Worcestershire sauce and sugar. Tip the tomato mixture carefully into the pan with sausages and return to a simmer.
Reduce the heat, cover the pan loosely with a lid and leave to simmer very gently for 20 minutes, stirring occasionally. Stir the beans into the casserole and continue to cook for 10 minutes till the sauce is thick.
Season with salt and pepper and serve warm.