I disagree. Departing in OW F does not guarantee access. Still surprises me so many people here think that it does, based on the occasional OW F passenger being granted access. I actually have yet to see a BA passenger granted access whereas I've seen plenty denied access.
The correct advice would be YMMV. Try your luck but it is NOT QR policy and it's misleading for people here to continue to promulgate unverified, incorrect information.