Rub the lamb all over with oil then cut small slits into the meat and fill with slices of garlic. Rub the meat will all the herbs, spices and some garlic powder. Finally combine the water and vinegar then rub over the meat. Cover the meat with cling film put it in a fridge from evening till morning.
Remove the lamb from the fridge and bring up to room temperature, this will ensure a more even cook.
Preheat the oven to 180 C / Gas 4.
Remove and discard the cling film then place in a roasting tin, season with salt and pepper. Cover with aluminium foil.
Roast in the preheated oven for 1 1/2 hours, checking from time to time.
Remove the foil and return to brown for a further 20 minutes. Remove from the oven, cover with foil and let rest for at least 10 minutes before slicing and serving.
For rare lamb the internal temperature will be around 50 degrees C, for medium-rare 60 degrees C, for medium 65 degrees C and for well done 70 degrees C.