Originally Posted by Paralytic

I think if you objected to the upgrade, you'd could be given your original seat back, so no refund would be due, but if you protested enough to the cabin crew and were told you had to sit in your new seat, I'm sure you could try to claim a refund.

However, that second option might result in you being given another seat in your original cabin due to someone else already having your old seat - in which case you would be due a refund.