Originally Posted by
Capricorn70
Do I need to book the Avios u/g at the same time via BA.com?
You can MFU/UuA subsequently if you want (eg if there's no award availability when you book the cash ticket but it opens up later), and you can do it on ba.com if it lets you, or you can always do it on the phone (but subject to a possible phone fee for non-Golds).