Hello everybody, I've got a simple question but I can't seem to find a definitive answer...can you help?

I've seen somebody mention in another thread that when they upgraded using Avios from CW to First, they had to pay the taxes & fees. Is that correct?

I'm just about to book some flights CW in I class. I have a feeling that because it's a non-flexible class, I'll have to pay taxes & fees for changing the booking at a later date (i.e. UuA to First).

I would be most grateful for some feedback,

cheers