Have a look at this thread

https://www.flyertalk.com/forum/brit...17-thread.html

To give you an indication of the £££s to pay for upgrade at airport. The airline may need to operationally upgrade for free depending on loads / overbooking etc. On the A380 you're in the mix with 100 other Club World passengers so odds aren't on your side. Gold is not always a good thing - plenty of reports of lower tier / never First passengers getting the upgrade over the highest value members... If you're willing to fork out £5/600 just do it at check in if it's available