I've doing the same RFS CE thing in a few days time from ABZ to CDG with a couple of weeks in London. On previous occasions, I've had mixed results. No problem at EDI, then was refused at MAN, and confusion at GLA. Not sure what to expect next week in Aberdeen.

My advice would be, if you really want lounge access, is to email BAEC beforehand with your flight details and explain that there seems to be confusion about the issue. I did this on my last trip, then was refused entry at T5 but then was allowed in once they saw the reply to the email.