You probably need to replace the keyboard then.
A new keyboard probably won't cost you much more than a tenner on eBay. Then you can either fit it yourself (following instructions that you'll probably be able to find on Youtube) or pay a computer repair guy to do it for you.
Don't use PC World though. They'll charge you around £30 for the part if you let them source it and then another £60 for fitting it. As I've said, you can buy the part yourself for around a tenner and pay a local repair shop about £30 to fit it (or perhaps less if you're lucky), or you can fit it yourself for free.
I replaced a laptop keyboard last night. The part cost me £9.97, with free postage. Fitting it involved nothing more than removing six screws, levering a panel off, unplugging the old keyboard, plugging the new one in and putting everything back together again. It took me no more than 5 minutes.