Hi
@davd,
The highish sugar content of the port may have very well contributed to the higher blood sugar levels you've seen. (Zero-carb alcohol in itself such as vodka, gin, whisky, rum will usually not drive up your blood sugar levels. Also dry wines will hardly move them.)
However, the potatoes, bread and biscuits will have been equally bad as the Port -- if not worse.
Non-diabetics would not see higher blood sugar levels regardless of what they eat or drink. So, personally I suspect that returning to eating bread, cakes, biscuits, rice, potatoes, cereals or drinking sweet beverages (even without the Port) would make you see diabetic blood sugar levels again.
You can always give it a try, though. In this case, however, I would recommend using a blood glucose meter to see the immediate impact of the change in diet rather than waiting three months or longer to see the effect on your HbA1c.