Heat oil in a large saucepan over medium heat. Add mushrooms,celery,carrots and onions and cook, stirring, until softened,about 5mins. Add flour,salt and peper and cook,stirring for about 2mins.

Add stock and bring to the boil, scraping up any brown bits. Add rice and reduce heat to simmer.Cover and cook until rice is tender, 5-10mins. Stir in chicken,sour cream and parsley and cook until heated though and serve.