The GHD is recommended highly, from what I've seen elsewhere, but I don't straighten my hair often enough to really warrant the price--if I did, that would be the one I'd go with. From what I've heard it's dual voltage (and actually works in that respect), so if you plan to travel back and forth it would be especially useful.
I'm worried about finding a decent three-barrel curling iron. I know it's not the most commonly used tool here in the US, so I have no clue what the market is going to be like for them in England. I know the one I have here at home would just immediately set a fire if it got within three feet of a UK outlet, so I'm not even going to try it.