Preheat the oven to 220C/425F/Gas 7.
Pound all the herbs, garlic and a few drops of olive oil into a mortar until you have a coarse paste, then add salt and peppercorns.
Lay the lamb skin side down. Slash the meat deeply with a sharp knife. Rub the herb paste into the cuts then lay the peppers on top. Roll the lamb up and tie with two or three pieces of cotton string (you don't have to do this). Rub any remaining paste on the outside. Roll into 3 or 4 layers of foil and bake for 1½ hours
After 30 minutes cooking, put the potatoes in. Lay a big sheet of foil down and place the new potatoes, parsnips, carrots, garlic, olive oil, lemon slices and any herbs left. Season well and seal up. Bake with the lamb for 1 hour.
Make the gravy mix the foil bag juices from the lamb with some flour and butter, add a little red wine, then whisk. Serve.