BA has quietly changed their online booking tool for awards to make it easier to find partner and connection awards. (This excludes reservations when using a Gold Upgrade Certficate).
The new page shows BA only options first, then BA and partner connections and then wholly partner connections all on the same page. In the previous version you could not choose partners unless BA had no availability.
This is a sample page for a dummy one-way to Tokyo:
This is good news as it saves several searches and you can find some fun connections if you like that sort of thing.
The other good thing is that you can see at a glance which other days have some form of availability – coloured light blue in the date field: