Put the pasta in a large pan and cover with salted boiling water. Bring back to the boil, stir once, then cook for 7 minutes. Drain and set aside in a 1 litre baking dish. Preheat the oven to 180°C/gas mark 4.
Meanwhile, melt the butter in a large pan and stir in the flour. Cook for 1-2 minutes to make a paste, then gradually pour in the milk. Over a very gentle simmer, whisk the sauce for about 5-6 minutes until it thickens.
Add the horseradish, paprika and cheese, reserving 1 tbsp for the topping, and stir until the cheese has melted. Season with freshly ground black pepper.
Pour the sauce over the drained pasta and mix well. Scatter over the tomatoes and mix the breadcrumbs with the reserved cheese before sprinkling on top.
Bake in the oven for 30 minutes and then put under a preheated grill for 5 minutes until the breadcrumbs have turned golden brown.