Preheat the oven to 170°C (fan oven 150°C), gas mark 3.
Line a 20cm (8in) square by 5cm (2in) deep cake tin with non-stick baking parchment. Keep the pears in a bowl of water with a squeeze of lemon juice until needed.
Put the flour and spices into a large bowl. In a cup, mix the bicarbonate of soda with the milk and set aside. Mix 2 tablespoons of the marmalade with 1 tablespoon of the black treacle, then set aside.
Place the remaining marmalade in a pan with the remaining treacle and the syrup, sugar, butter and ginger. Pour in 150ml (1/4 pint) water and heat gently until melted.
Beat the marmalade mixture into the spiced flour along with the oatmeal, followed by the eggs and milk. Pour a thin layer of the cake mixture over the base of the tin and bake in the preheated oven for 10 minutes.
Drain the pears. Take the tin out of the oven and push the pears into the base. Pour the remaining cake mixture around them and return to the oven for 1hr and 25 minutes.
Warm the reserved marmalade and treacle mixture in a small saucepan and brush over the hot cake to glaze. Serve warm or cold.
