Take your turkey crown out of the fridge 1-2 hrs before you want to cook it. Heat oven to 200C/180C fan/gas 6. Cut 4 slices from one of the oranges. Juice the rest of it along with another of the oranges. In a small bowl, stir the orange juice together with the honey and the picked thyme leaves, the soy sauce and a good grinding of black pepper.
Loosen the skin over the turkey breast. Place two slices of orange, a bay leaf and thyme sprig under the skin, on both sides of the breast, then spoon in some of the juice mix and smooth the skin back over. Tip the orange wedges into a roomy roasting tin with the carrots and parsnips. Nestle the crown amongst the vegetables and oranges. Drizzle over about a third of the remaining orange juice mix and roast everything in the oven for 30 mins. Remove, give the veg a stir and drizzle over another third of the juice mix, then return to the oven and do that again one more time, roasting the turkey for a total of 1hr 30 mins (covering with foil halfway through if it begins to colour too much).
Remove the turkey from the roasting tin and place on a board covered with foil, then turn the oven up to 220C/200C fan/gas 8. Toss the veg in a drizzle of honey and put the tin back in the oven to caramelise the veg for 25-30 mins, leaving the turkey crown to rest. Serve the crown on a platter surrounded by the glazed roots, orange wedges and extra thyme sprigs, if you like. Remove the sticky skin from the breast before carving the meat to serve as a side.