Zoyabean, a couple of things. You said you were taking your hard drive out to bring with you. If you were hoping to take out the hard drive from a Windows machine, bring it over, buy another computer, stick the drive in, and hey presto! your Windows system is reconstituted, this won't work.
However, if you were thinking of bringing over all your files and stuff so you could have access to them that would work. One thing to really consider is that it is better to get an external hard drive case with its own power supply (brick or wall wart) because this is better for the computer it is attached to. So you have the 120 volt 240 volt thing. You can buy cases in the UK cheaply so maybe you just need a box and some polystyrene granules.