Peel and crush (mince) the garlic, then mix all the marinade ingredients together. Rub this mixture into the outside of the beef then cover and leave for at least two hours (preferably overnight) in the fridge, to absorb all the flavours.
Place the beef in a roasting tin and cook in a preheated hot oven (Mk 7 - 425ºF - 220ºC) for 30 minutes. Baste the meat with the juices, and turn the oven down to moderate (Mk 3 - 325ºF - 170ºC). Cook for a further 30 minutes per Kg (14 minutes per pound) to give you medium-cooked meat (see our Roasting Guide for more information).