Dust the diced lamb neck and kidneys in the flour and season well. Melt the butter in a large frying pan over a medium heat. Add the garlic and cook for 2 minutes then add the lamb and stir to brown on all sides.
Remove the lamb and transfer to a lidded ovenproof casserole dish. In the same frying pan, add the onions and carrots and cook and stir for 3 to 4 minutes. Transfer to the casserole dish and add all of the other ingredients, except the potatoes, and give a good stir. Lay the sliced potatoes on top of the lamb mixture and season again. Cover.
Bake in the preheated oven for 1 hour then remove the lid and bake for a further 30 to 40 minutes to allow the potatoes to become golden brown. The lamb should be tender and the filling piping hot. Remove from the oven and serve.