Don't think anyone has mentioned this.....
I was in the WHSmith library at lunch flicking through a copy of Ride and it seems that Oxford are offering to replace any of their cylinder locks that are deemed to be problematic ie the ones you can open with a biro. It said in the article that you don't need your receipt. What it didn't say was how you go about changing the locks but it did mention going into their dealers who would swap the offending item, may be worth giving oxford a call first though. HTH
Steve