You are entitled to the TPs and avios for the underlying cash fare, so in this case for the WTP fare. If you just AUP/POUG your WTP fare you would be entitled to the upgraded cabin TPs and avios. However, once you GUF/UuA you break that link.
Of course mistakes can happen and with BA IT you may end up with more that WTP, but I wouldn't broadcast it if you do
