Roll the grouse pieces in the flour seasoned with salt and pepper. Melt the butter in a large heavy frying pan, and brown the grouse on all sides.
Put the grouse and all the other ingredients except the tomatoes in a large casserole dish. Add the boiling water, then cover and simmer for 1 1⁄2–2 hours. Add the tomatoes and continue to simmer for a further 1 hour. Serve hot.