Yep all you have to do is flip the switch on the back next to the plug in. I would spend the two quid on a British cord, a computer isn't something you want to use a plug adapter with. I would worry more about the monitor. One gorilla baggage handler or a sharp object hitting the screen will screw it up good. When you get there, if you are the handy sort, open up the computer and make sure nothing has worked loose before powering it up. If you touch anything inside, be sure to ground yourself by touching the power supply (the metal box with all the wires coming out) or metal part of the case first.

Games usually have DC adapter, all it takes is matching the DC output on a British wall wart. ASDA or some other store is bound to sell those. The only thing is most British televisions have a SCART connector rather than the RCA connectors we use. There are adapters for those as well.

Have a great time!