In large skillet, heat oil over medium-high heat. In 2 batches, add beef and cook each batch 3 to 5 minutes or until beef is browned, stirring occasionally. Transfer beef to 5 to 6 quart slow cooker.
Add potatoes, thyme, garlic, leeks, bay leaf, onion, broth, carrots, barley, parsley, and Worcestershire sauce. Cover and cook on low 7 to 8 hours or until beef and potatoes are tender.
In medium bowl, whisk together water, and flour; stir into slow cooker. Increase heat to high, cover and cook 15 minutes. Stir in peas, and vinegar; cover and cook 3 minutes. Remove and discard bay leaf, and thyme stems. Season with salt, and pepper. Serv