The charger cubes that come with iPads are dual voltage.. You can use them for both 110 and 220 volt mains.. The only problem you'll have is that the plug won't fit in the UK wall socket. You'll have to get a North America to UK adapter... I'm not sure about the 4s charger.. It won't hurt to try it. If it doesn't have enough juice, you'll get a "Not Charging" message appearing near the battery indicator on the iPad.