Given the increased overcrowding on the FGW Thames Valey routes, and the fact that my travel expenses allowance has just been increased, I'm tempted to change my annual gold card from Twyford to Paddington from standard class to first class. However I'm only 4 months in to the run of the standard class gold card. Would I be able to upgrade the rest of the validity of the gold card to first class pro-rata without losing gold card privileges? Those leather HST first class seats are just too tempting!!!