Preheat the slow cooker if necessary; see the manufacturer's instructions. Heat the butter and oil in a large frying pan, add the diced venison a few pieces at time until all the meat has been added, then fry until evenly browned. Transfer to a plate.
Add the onion to the pan and fry for 5 minutes. Stir in the mushrooms, garlic and flour and cook for 1 minute. Stir in the wine, stock, tomato purée, redcurrant jelly, peppercorns and salt and bring to the boil.
Arrange the venison in the slow cooker pot, add the hot wine mixture and press the venison below the surface. Cover with the lid and cook on low for 8–10 hours.
When almost ready to serve, make the scones. Put the flour in a bowl, add the butter and rub in with the fingertips until the mixture resembles fine breadcrumbs. Stir in a little salt and pepper, the cheese and herbs. Reserve 1 tablespoon of egg for glazing and add the rest. Gradually mix in enough milk to make a soft dough.
Knead lightly, then pat the dough into a thick oval or a round that is a little smaller than the top of your slow cooker. Cut it into 8 wedges and arrange, spaced slightly apart, on top of the venison. Cover and cook on high for ¾–1 hour.
Lift the pot out of the housing using oven gloves, brush the scones with the reserved egg and brown under the grill. Serve with green beans, if liked.