I am afraid GPR and GUFs can't be used together.
https://www.britishairways.com/en-gb...ditions-of-use
Gold Priority Reward
....
7. Gold Priority Reward may not be used in conjunction with [i] Avios & Money, [ii] Gold Upgrade for One or Gold Upgrade for Two; or [iii] Avios for Upgrade or [iv] American Express Vouchers.