UK vs US power supplyPower comes out of UK wall sockets at about 220 volts (actually 220-240). The the alternating current cycle is rated at speed of 50Hz. In North America, power is supplied at 110-120 volts and alternates at 60Hz. Except for microwave ovens, clocks and products with sensitive timing mechanisms, most North American devices can operate at either 50 or 60Hz. Voltage is another matter.
If you plug in devices designed for use in North America, not only won't they work, they may explode. At the least, they will certainly set off a rather fine fireworks display before they self-destruct.
The dual-voltage solutionYou'd be surprised at how many of the electrical devices you'd expect to take on vacation are dual voltage. Hair dryers, shavers, travel irons and clothes steamers all now come in dual voltage versions that can be switched over to 220-240 volts when you pack.
Laptop computers and other modern electronics are usual made to operate at dual voltages and will switch over automatically. And battery chargers for camcorders, CD players, cell phones and other battery operated devices can almost always be plugged into English sockets (with an adaptor plug), even when the devices themselves cannot.
To be sure, check the rating, usually on the bottom of the product, or its AC adaptor. If it says "Input: AC100-240V", as in the picture above, you are safe to use it in the UK. You'll need an adapter plug though. They're inexpensive and easy to find from travel suppliers.