In a bowl, sieve together the flour and spices. Add the suet, breadcrumbs, lemon rind, sugar, nuts and dried fruit.
Warm the treacle in a pan until it becomes runny. Add the rum, stout and lemon juice. Pour over the eggs and mix together. Add to the dry ingredients. Mix thoroughly, cover and stand overnight.
Add a little milk if the mixture has stiffened. Preheat the slow cooker for 20 minutes. Turn the mixture into a buttered 1 litre pudding basin or a basin which comfortably fits in the slow cooker without raising the lid and cover with foil. Stand in the slow cooker and add enough boiling water to come up the sides of the basin.
Cook on HIGH for 13 hours. Allow to become cold.
Remove foil and cover with greaseproof paper and fresh foil.
Serve warm with plain or brandy custard.