It looks like an O2 employee might have accidentally let slip the iPhone5 release date to a customer. A reader has reported in to the site Know Your Mobile that they rang O2 customer services enquiring about the iPhone5:

The customer service representative told our tipster that the iPhone 5 would be getting release on October 21

This ties in with the rumour of an iPhone5 announcement on 7th October allowing exactly 2 weeks until the device then comes available. It seems unlikely that a CS rep from O2 would give out the date, unless it was a complete accident, but the security surrounding the release date would most probably be drummed into all employees so this one could have a short career if it really was a goof.