Heat olive oil in a large heavy-based saucepan over medium heat, add duck and cook, stirring, for 6-8 minutes or until brown, then transfer duck to a plate. Add onion and garlic and cook for 5 minutes or until tender, then add herbs, carrot, celery and cook, stirring, for 3 minutes.
Add tomato paste and cook for 5 minutes, then add potatoes and chicken stock. Return duck to pan and bring to the boil. Season to taste with sea salt and freshly ground black pepper. Partially cover with a lid and reduce heat to low, simmer for 3 hours or until duck is tender. Stir through peas and cook for 5 minutes. Ladle stew into bowls and serve.