Preheat the oven to the highest setting. Bring the lamb up to room temperature.
Prepare the paper package by cutting three 1 metre long pieces of baking parchment. Lay each sheet over the other in three layers. Cut two long pieces of foil and place on top of the paper. Place a roasting rack inside a roasting tin then lay half of the paper and foil (the foil only needs to be under the lamb) over the rack and allow the other half to hang over the edge (this will be folded over the lamb in step 4).
Score shallow indents in to the lamb. In a frying pan over a high heat, warm half of the oil and brown the lamb on all sides. Remove from the pan and allow to drain on kitchen paper.
Place the potatoes carefully on top of the foil then place the browned lamb on top of the potatoes and rub with the remainder of the olive oil then rub in the garlic, herbs, lemon zest and juice, and season liberally. Crush and sprinkle over the bay leaves. Bring the sides of the foil up around the potatoes (this is to help hold in all the juice). Fold the other half of the paper over the lamb and roll or fold the edges to seal.
Roast in the hot oven for 20 minutes. After 20 minutes, lower the heat to 180 C / Gas and continue to roast for a further 60 minutes.
Remove from the oven and allow the lamb to rest for 25 to 30 minutes (keep the parcel sealed). After resting, cut the parcel open, carve and serve.