Your best bet is to try and get a part-time job at a fast food retaurant(like MacDonalds or similar)..how many days/hrs you want to work will depend on the manager at the store OR how quickly you want that brand new computer.
Doing so will allow you to...
a) make some quick cash and at the same time learning and understanding what it takes to make a buck(or a pound in your case):y:
b) improve on your socialising skills:y:
c) make some friends:y:
d) hey,ya might even find your future g/friend there!
Some people frown at working at these fast food outlets or too embarrassed because their friends might see them there.unless you're born rich,pride,my friend,will get you nowhere in this day and age.make your own decisions,do what you think is necessary to make the money(legally) and whoever(apart from your parents..always listen to your parents) thinks otherwise,give them the middle finger! lol
Good Luck bud.