According to this response in their CC verification FAQ, a credit card can be verified at any office. Perhaps you can ask them to validate immediately at the Qatar office when you go down?
https://qatarairways.zendesk.com/hc/...t-should-I-do-

Alternately, you might be able to place a hold on the itinerary and then your uncle could to go to the London office himself to pay on his own card.