Correct me if I'm wrong but SIBA is a trade organisation for brewers, and I quote from their website 'formed in 1980 as the Small Independent Brewers’ Association, to represent the interests of the emerging new wave of microbrewers'.
As such they will push their product and encourage all to drink it in the same way as the big brewers did in the past. They may well have a kegged beer festival this weekend, presumably to try to convert us all to keg beer as, as has been mentioned before, kegged is easier to keep that cask ales etc etc.
CAMRA is an independent organisation, not funded, nor therefore influenced, by the brewers. CAMRA's mission is to protect the interests of cask ale drinkers.
Like someone (OB?) said of CAMRA, their competition, their rules.