Place the sugar, malt extract, treacle and butter in a pan and heat gently until the butter has melted and the sugar has dissolved. Leave to cool.
Mix the flours, salt, yeast and sultanas in a mixing bowl.
Pour in the cooled malt syrup mixture and the warm water. Mix thoroughly; the mixture will be soft and sticky.
Turn the mixture onto a floured surface and knead gently for a few minutes to bring the mixture together.
Grease two 450g/1lb loaf tins and divide the mixture among them. Smooth the mixture with the back of a spoon so that the top is smooth and level. Cover each tin with a plastic bag so that it is loose and not touching the top of the tin. Leave for a couple of hours, or until the dough has risen to the top of the tins.
Preheat the oven to 190C/375F/Gas 5. Remove the plastic bags and bake for 30-40 minutes. If the top of the loaf starts to brown too quickly, cover with a sheet of foil and continue baking.
Remove from the oven and brush the top with warm honey to glaze. Cool on a wire rack.
Slice and eat with butter.