Preheat the oven to 220°C / 200°C fan / gas mark 7 / AGA roasting oven.
Place the onions, carrots, fennel, potatoes and sausages in a large baking tray. Drizzle with 1 tbsp olive oil, season with a little salt and lots of freshly ground black pepper and toss together.
Roast for 20 minutes, take out of the oven and turn the veggies and sausages. Return to the oven and cook for 15-20 minutes until all are starting to crisp in places and the sausages are nicely browned.
While the sausages and vegetables are cooking, mix the remaining 1 tbsp. of olive oil with the thyme, marmalade, mustard, honey, salt and pepper.
Take the tray out of the oven once more and drizzle over the marmalade mixture. Gently toss together and return to the oven for 10 -15 minutes until everything is sticky and golden.
Serve immediately with a green vegetable or salad.