Heat oil in large flameproof casserole pan to a medium heat (not too high so onions don't burn!)
Fry onions, celery and chillies until onions soften (approx 10 min)
Increase heat, add beef mince, and cook until browned, stirring constantly
Pour out excess fat (if any) into old container
Add chilli powder, ground cumin, and tomato puree. Mix well for a minute.
Add sugar, worcester sauce, oregano, stock and tomatoes. Stir well and bring to boil.
When boiling, lower heat to a gentle simmer and cook for approx 40 min until ready
If you wish to add kidney beans, stir them in 10 min before the end