Originally Posted by
LondonCanuck
... What you have to remember is that there will be some additional taxes for you and your companion, but also that the infant won't be covered using the GUF2, but rather will pay a cost of 10% of the cash ticket for CW (the class you are upgrading to), rather than PE...
Good point - using the numbers above in post#2 the actual differential looks to be 255 (taxes/surcharges) + (2*(100-30)) = 140 as the difference in infant fare).
That gives 395 GBP, so still a bit less than the 560 GBP mentioned in the original post, but maybe there is only a higher CW fare (for the infant) available on the dates in question.