Heat half the oil in a large pan over medium-high heat. Add onion and garlic and cook for 3 minutes, stirring regularly – place in the slow cooker.
Heat the remaining oil and add beef. Cook for 3-4 minutes until evenly browned. Add to slow cooker.
Add vegetables, beef stock, tomato paste, worcestershire sauce, and herbs and mix well.
Cover and cook on high heat for 4 hours.
Whisk together flour and a small amount of stew liquid in a small bowl to make a paste. Ensure it is lump-free. Add the paste to the slow cooker and stir well to combine.
Cover and cook on high heat for a further 30 minutes
Top with fresh parsley and serve.