Preheat the oven to 220°C / 425°F / Gas mark 7.
Crush the chilli, garlic, and half the rosemary in a pestle and mortar with a generous pinch of salt and black pepper.
Grind together to form a rough paste, then add the fennel seeds.
Make slits in the lamb, then rub the paste over the meat, pushing it into the slits as much as possible.
Drizzle with oil and season with salt and pepper.
Scatter the remaining rosemary over a large roasting tray and sit the lamb on top.
Put the lamb in the oven.
After 20 minutes reduce the oven temperature to 200°C / 400°F / Gas mark 6.
Add the wine and a splash of water and then roast for 1 hour 15 minutes (or 15 minutes per 500g) for medium, or 1 hour 35 minutes (or 20 minutes per 500g) for well-done meat.
Baste the lamb a couple of times during cooking, then, about 15 minutes just before the end, pour 110ml of water into the tin, baste again and return to the oven.
Remove the lamb from the tin, transfer to a serving plate and leave to sit for 20 minutes.
For the gravy, spoon off any excess fat from the cooking juices, then place the roasting tin over a high heat on the hob.
Scrape any sticky bits from the bottom of the tin with a wooden spoon, then add the flour and whisk.
Add the stock and leave to bubble for 3-4 minutes.
Stir in the jelly, season with salt and pepper then add a little more water or stock to reach the desired consistency.
Slice the lamb thickly and serve with the gravy, some rosemary if using and of course any green vegetables preferred.