If I ship something back to the U.K., that was purchased in the U.K. and has already had VAT paid on the goods, I'm still gonna have to pay VAT, right?
Nope. I did this. Shipped personal items (that I bought in the U.K. and owned for years) back to the UK from USA. There is a form I had to fill out and attach to the outside of the boxes. They never even looked at the forms as they were still attached to the boxes when they arrived at my parents in the UK.
I also took a bike (on the plane) to USA then back to UK after a long time. I just walked through customs. Not sure how they could prove where it originated from.