The iPad should work fine. And, they are dual-voltage devices, so you can put a plug adapter on the USB cord you get from the seller (cause one should come with, right?). Or, you can buy a country-specific USB cord from your local Apple store...
There are two iPads you can buy to use 3G - one that has a GSM chip and one that uses GSM and CDMA chip. As far as I understand, they both should work in the UK.
At this point, all you can do is try it. If it works, yay! If not, then send it back.
Marilyn