You will need to check the fare rules specific to your ticket as to the change fees.
There also needs to be T availability for the other flight (which there is for BA173).
Originally Posted by
IdiotAbroad
I have successfully UUA'd a T class fare. You'd also need to pay the £100 difference for the time change. So c.£145 and 10k avios.
Not all T class fares have the same change fees. Some are completely non changeable non refundable.