Originally Posted by danielbk

When you book via a travel agent it goes into a revenue booking, the from class is irrelevant, only what you are upgrading into.

So T for WTP
I CW
A First

The amount of payment is calculated as the lowest possible legal fare for the underlining class of service at time of booking (not the lowest available, so you can pay for I class even if it wasn't available at the time you upgraded to A)