I need to cook a leg of lamb but have no oven. I do have a steamer but this is too small for the leg to fit into. The leg is fairly large as it has to feed 14 people. I do have a hob and a grill.

You can cook lamb "low and slow" on the grill using an offset charcoal method. Temp should be about 250 and the lamb should not rest directly over the coals. You'll need a thermometer to check the internal temp. 160 F would be a nice medium temp. I'd rub it with something like rosemary, garlic, salt and olive oil. When it's close to done I'd wrap it with foil and add a liquid like red wine. Take it off the grill when it reaches your target temperature and leave foiled for a minimum of 15 minutes. You can play around with the spices to suit your tastes. This slow grilling and foiling method will produce a pretty tender result.