Originally Posted by
KARFA
You don't need avios to do a dummy booking. Just sign in to your BAEC account, go to booking a flight with avios, and do a dummy booking. If you don't have enough avios it will obviously warn you of that on the quote page and not let you book it, but it will show you how many avios and how much taxes & fees are due.
Great, thanks KARFA, I didn't even try that as I assumed it wouldn't be possible!