I don't mean to sound harsh but I would try and forget of any upgrade to First just because of your Gold status. Sure, if it is overbooked you might have a small chance however the thread below is more useful although it is not gauranteed there will be any seats to sell as not very flight has them for 'offer' so to speak.

Good luck though!

http://www.flyertalk.com/forum/briti...17-thread.html

ETA: Lots of quick replies already!