Cook the potatoes in lightly salted boiling water for 15-20 minutes or until tender. Meanwhile, put the smoked haddock in a large shallow microwaveproof dish and pour over the milk. Cover with cling film, pierce a few times, then microwave on High for 4 minutes or until the fish flakes easily. (Alternatively, simmer in a pan on the hob for 5 minutes.)
While the fish cooks, heat 1 tbsp of the oil in a frying pan and fry the onion, ginger and paprika for about 5 minutes until the onion is soft. Remove from the heat.
When the potatoes and fish are ready, drain them both. Mash the potatoes with a potato masher, and remove the skin and any bones from the fish. Mix the potatoes, fish and onion with the coriander, lemon juice and plenty of salt and pepper. Divide the mixture into eight, roll each portion into a ball and flatten slightly. Dip into the beaten egg, then coat with the oats. Put on a plate, cover with cling film and chill in the fridge for half an hour or so to firm them up a bit.
Heat 2 tbsp oil in a frying pan (preferably non-stick if you have one) until very hot. Fry 4 fish cakes at a time for 5-6 minutes on each side, turning once, until they are golden and crisp. Lift out and drain on kitchen paper. Wipe the pan clean with kitchen paper and fry the remaining fish cakes in another 2 tbsp oil, making sure it’s really hot before you put them in. Serve hot, with lemon wedges and a cucumber and yogurt dip (bought or home-made).