Grease and line a 2lb loaf tin with non-stick baking paper (or use a non-stick loaf liner). Preheat the oven to 190C (170C fan) / 375F.
In a mixing bowl, whisk together the sugar, syrup, oil, milk, vinegar, orange extract and orange juice until fully combined. Stir in the orange zest.
Sieve one third of the dry ingredients (flour, baking powder, salt) into the bowl and whisk to combine. Repeat with the remaining two thirds, whisking each time. Stir in the poppy seeds.
Tip the mixture into the prepared tin. Place on the middle shelf in the oven and bake for 50 minutes, or until a skewer inserted into the middle comes out clean.
Whisk together the drizzle ingredients. When the cake is baked, pierce all over with a skewer. Distribute the drizzle evenly over the top of the cake. Allow to cool in the tin for at least an hour (it will firm up as it cools), then transfer to a wire rack.
Once completely cooled, slice and serve or transfer to an airtight container. The cake will keep for a week in the refrigerator. It also freezes really well.