A new software update that brings Android 4.0.4 ICS OS is now reportedly rolling out to GALAXY S II I9100G variant in the United Kingdom. The new firmware build is i9100G XXLPY and it you can upgrade through Samsung Kies software tool. It could also push out OTA (over the air), however we can not confirm it yet.
To check for the new build make sure you have the latest Kies software version installed on your PC/Mac, plug-in your phone via USB cable and check for updates. For OTA check go into Settings > About phone > Check for updates.