When I started with BA, it was common-place for check-in staff to make recommendations as "SFU" (Suitable for Upgrade) or "NSFU" (Not Suitable For Upgrade) and a proportion of these may ba acted upon if "Operational reasons" (overselling in economy) led to the need to move some fortunate pax into the forward cabins.
In recent years, the selling of the forward cabins has improved, to the extent that we no longer over-sell the economy cabin as much and the use of computers enables the back-office boys to reward our Gold / Silver card holders or High-Yield passengers - these are usually earmarked in the Check In computer system for us to contact the back office.
That having been said, notice is still very much taken of the "NSFU" remark - rude or aggressive behaviour, wearing scruffy clothing or making excessive demands may very well result in you never being aware that you had been considered for the magic seats! In the event you were commented as a "contact back office" - the check in agent will contact them after you have left the desk! with a "definitely not" remark! (I've done this quite a few times recently - don't know if something is in the air or not, but people generally have seemed so rude in the last few weeks! .......anyone else noticed this???)