Squeeze the sausages into a bowl or tip in the sausagemeat. Add the garlic, parsley and egg, and squish through with your fingers to mix everything well.
Lay a large sheet of baking parchment on your work surface. Use the bacon to make a large rectangular lattice, weaving the rashers in and out of each other. Place a piece of baking parchment on top, then use a rolling pin to roll over the bacon and seal the rashers together.
Butterfly the turkey breast by cutting into one side of it so you can open it like a book. Cover with cling film and use a meat mallet or rolling pin to gently bash it out into a rectangle that fits inside the bacon, with a 2.5cm border of bacon on each side.
To build the bombe, peel the top layer of parchment off the bacon, leaving it lying on the bottom sheet. Arrange the turkey, skinned-side down, on the bacon, then pat the sausage mixture on top. Trim the rounded ends off the chorizo and line them, ends touching, along the middle of the sausage meat mixture. Use the edge of the baking parchment to lift and roll the bacon and turkey into a tight log. Tie the bombe at intervals with string to keep it together, then wrap well in cling film and put in the fridge. Can be prepared, up to this point, and chilled two days ahead.
To cook, heat oven to 200C/180C fan/gas 6. Remove the cling film, then brush the bombe with a little oil, put it seam-side down on a baking sheet, and roast for 30 mins until the bacon has crisped up, then reduce oven to 180C/160C fan/gas 6.
Brush with the maple syrup to give it a sticky finish and continue to roast for another 45 mins or until the middle of the bombe reaches 75C on a digital cooking thermometer (check after 30 mins as oven temperatures do vary). Leave to rest for at least 15 mins before carving into thick slices. Any leftovers are delicious cold. Save the juices from the tin to make gravy.