Thanks all for this. I called back, different call handler and they upgraded me.

It did teach me some strange things about the BA booking process. Firstly, I quoted to upgrade at the same time as booking. That would have cost $600 more on a return ticket than booking into PE then upgrading separately.

Secondly, the BA website prices tickets differently depending on the class you request when searching for prices from the home screen. If you request Premium Economy, it prices seats in that class higher than if you request seats in Economy and then click on the Premium option.

AARP discount was not available for some reason but 10% for visa was.