In a large frying pan or skillet heat 1 tbsp of the oil over a medium heat. Add the onion, celery and garlic and cook for about 10 minutes, stirring frequently, until the onion is golden.   Transfer to the slow cooker.

Season the meat with salt and freshly ground black pepper. Heat another tbsp of oil in the frying pan or skillet over a medium to high heat.   Add half of the meat and cook for about 5 minutes, stirring frequently, until browned.   Transfer to the slow cooker with the onion mixture.   Repeat with the remaining oil and meat and transfer it to the slow cooker with the rest of the meat and onion mixture.

Add the potatoes, carrots and stir in the stock, tomato puree, Worcestershire sauce, thyme and pepper. Cover and cook on low for 10 to 12 hours, or high for 5 to 6 hours, until the meat and vegetables are tender.  If using low, turn to high.

In a small bowl combine the flour and butter. Stir the butter mixture and peas into the beef mixture.   Cover and cook for 10 to 20 minutes, until thickened.   Season to taste, and serve.