Preheat your oven to fan 180C/conventional 200C/gas 6. Cut the potatoes into halves or quarters depending on their size and put them into a large roasting tin. Drizzle with the olive oil and roast for 10 minutes.
Take the tin out of the oven and snuggle the sausages in between the potatoes so they sit on the bottom of the tin. Now roast for another 15 minutes, turning the sausages over at half time so they brown all over.
While you’re waiting for the sausages to cook, gently heat the marmalade, mustard and cider in a small pan, stirring all the time until the marmalade has melted. Increase the heat and boil for a few minutes until reduced by about half.
Pour the sauce over the sausages and potatoes and toss gently together. Scatter the rosemary sprigs on top, return to the oven and cook for a further 10 minutes until golden brown and sticky with the glaze. Sprinkle with salt and coarsely ground black pepper before serving.