Sorry for any confusion caused i will try and clarify.

There are two ways to book on the BAEC website excluding a standard book with cash option. Using the language of the site, the first is to "book with avios" and the second is to "book and upgrade". The first option looks for reward seats in each class. For my travel itinerary there are none (LHR=YVR 9th Oct Rtn anytime between 21-30 May). However when you do the second option i.e. "book and upgrade" and tick the box to upgrade the inbound only it gives me 8 "reward seats" (their words) in WT and 6 in WTP on the outbound and numerous on the inbound (which would now be a Club ticket due to the 12500 avios).

So although my poor sentence construction may have caused confusion it is actually BA who are using the terms "reward seats" in both instances regardless of whether you are using avios to actually pay for the ticket or merely using avios to upgrade a cash ticket.

My confusion is in the fact that if i book with cash the flight on the 9th is £608 and 1458 for WT & WTP respectively (as part of a return fare). However when i go to book using the "book and upgrade" function it suggests i can get WTP outbound and Club on the inbound for 12.5k avios and £1140rtn. This suggests that the "book and upgrade" system used on BAEC website has a mind of its own and isn't simply upgrading a cash ticket with avios as this "book and upgrade" fair is lower than a single leg when paying in cash.

Is that at all clear?