Preheat the oven to 180C/350F/Gas 4. For the roast leg of lamb, place the leg of lamb on a clean work surface or chopping board.
With a long, thin, sharp knife, make lots of incisions all over the meat.
Insert the strips of ham and rosemary together deep into the incisions leaving a little out.
Rub the olive oil all over the lamb and season with salt and pepper, rubbing well in.
In a bowl, mix together the parmesan or pecorino and breadcrumbs.
Carefully sprinkle over the top and side of the lamb and press well with your hands so the meat is well covered and the crumbs don't fall off - if some do, just gather them up and place onto the meat.
Carefully place the meat in a roasting tin which will just fit the lamb. Pour in the wine and water on the side of the tin (not on the meat).
Cover with foil and place in the preheated oven for about two and a half hours, which will give you a medium- to well-cooked lamb. Cook for less time if you prefer your lamb pink.
During cooking, check from time to time the liquid content - if necessary add more water. For the last 10 minutes of cooking time, remove the foil and increase the heat to 200C/390F/Gas 6 and roast until the topping goes golden and crispy, but be careful not to burn.
Remove from the oven, slice and serve. Don't forget to pour the cooking juices over the lamb slices if you desire. Serve with small roast Jersey potatoes with the skins on, and the peas with pancetta.
For the fresh peas with onion and pancetta, heat the olive oil in a saucepan, add the onion and pancetta and sauté.
Stir in the peas and stir fry for a couple of minutes. Add the stock, bring to the boil, then reduce the heat, cover and simmer for approximately 20 minutes, stirring now and again.
After this time, the stock should almost have evaporated.
Serve immediately or make in advance and re-heat when required.