Heat oil in a large frying pan over medium heat. Add celery and carrot and fry for 3-4 minutes until celery is softened. Add to slow cooker.
Fry sausage pieces 3-5 mins until browned on the outside. Add to slow cooker.
Add tinned tomatoes, tomato paste, stock cube and 1 cup boiling water to slow cooker. Add onion marmalade and cubed potatoes, season with pepper, cover and slow cook on low for 8 hours.
When ready to serve, season with salt if necessary. Serve spooned over cooked pasta.