Live report: on the phone to BA now, being told that this is an Avios change fee and nothing to do with offline service fees. I am pursuing the line of "we upgraded, it wasn't a change to the date/time of the flight"...

I'm going to refer them to this page, which says nothing about upgrade fees http://www.britishairways.com/en-gb/...d-service-fees

FlyerTalk saves the day again: just got our £71 refunded, thanks all especially Paralytic