You can plug most US laptops right into a UK electrical outlet. Check the sticker on the bottom of the computer (or on the transformer). It should say something like "Input: 112V/240V, 50/60Hz" If it says that, all you need is a plug adaptor. If it ONLY says 100 or 110 or 112V, then you will need a transformer, otherwise the thing will fry when you plug it into a European circuit. But that situation is quite rare; I think all new US laptops work on all currents.