Preheat oven to 350 ºF. Clean chicken and pat dry. Season cavity of chicken with salt and pepper. Scatter vegetables over bottom of roasting pan. Mix butter with thyme and garlic and rub over outside of chicken. Season outside with salt and pepper. Place the chicken on the vegetables and cover with aluminum foil. Bake covered for an hour. Remove foil and bake for another 1/2 hour. Baste regularly. Remove chicken from pan and let rest. Strain the juices from the roasting pan and reserve. Place the roasting pan over medium heat, add the reserved juices. Add the flour, scraping bottom of pan with a wooden spoon. When the flour is a thick paste, slowly add the beer and chicken stock while whisking. Serve the roast chicken with peas and green beans, warm gravy and a pint of Belhaven Best Ale.