I *think* this is a married segment issue and you won’t be able to upgrade just one leg. Your options are POUG at the airport or a B2B day trip to NCL, EDI, GLA etc to get the TP.

BA *may* let the 10 TP slide or give you the extra 2 weeks grace to earn the 10 TP needed as back ups but plan accordingly if Gold is that important to you.