Heat the oil in the pan. Season the oxtail well with salt and pepper. Brown on all sides in the pan, turning frequently for about 10 minutes, then remove and set aside.
Pop the chopped onion, celery and minced garlic into the pan. Sauté for about five minutes until soft and browned, then add the flour. Reduce the heat, stir for a couple of minutes, then mix in the tomato paste.
Return the oxtail to the pot and pour in the stock. Stir in the bay leaves, rosemary, thyme, salt & pepper. Bring up to pressure for 40 minutes.
Remove from heat and, when the pressure's dropped, take off the lid. Carefully skim the fat from the top of the stock and discard.
Add the potatoes, carrots, Worcester sauce & chilli. Pressure cook for a further 10 minutes.
Garnish and serve hot with crusty bread.