Might be unrelated, but see my thread http://androidforums.com/samsung-galaxy-s2/394688-sudden-increase-data-usage-how-do-i-find-out-cause.html
I had 138.13 MB used in one day which I narrowed down to one app running without my knowledge. The app is AP Mobile. It does not
need to be on your home screen to be actively downloading updates. I too am on Orange, but I don't think my issue was network provider related. If you have the app on your phone, use Traffic Stats Lite or My Data Manager to monitor how much data it is using (and it's worth checking your battery stats as it can eat that too).
This app does not appear to be a problem for all users, but it certainly has been for some.