Heat oven to 160C/fan 140C/gas 3. In a large, deep roasting pan, gently toss everything, except the basil, together, then season.
Place the vegetables in the oven, then roast for 2 hrs, undisturbed. Remove from the oven and leave to cool. If you want, drain the vegetables before serving and serve their juice on the side, or simply stir through the basil and correct the seasoning.
The vegetables can be roasted up to 2 days ahead. Cover and leave in the fridge, but bring out at least 4 hours before serving so the vegetables are served at room temperature.