Place a large casserole dish on a high heat. Add a dash of Olive oil followed by the cubed mutton. Season the meat with salt and pepper and fry on all sides until it’s beginning to colour, about 4 – 5 minutes. Add the sliced onions, the garlic and the rosemary and continue to cook, stirring as you do, for 8 - 10 minutes. Pour over the stock and bring to a gentle simmer. Cook the mutton, with a lid set just ajar, at a very low, tremulous simmer about 1 ½ hours. Now add the rinsed barley and continue to simmer for a further 40 minutes. If the stew looks a little dry then add a dash of water. When the meat is lovely and tender add the samphire, bring the stew back to a simmer and cook for 5 – 10 minutes. Taste and adjust the seasoning. Remove the pan from the heat and allow to sit for 5 minutes before serving.