How is your credit? My suggestion would be to just buy a computer on credit and pay it off. A £1200 computer you could have easily paid off in a year. Just a suggestion. I imagine leasing a computer is much like leasing a car (expensive is restrictive).
I ask because my University used to lease out laptops to students for a good price. They were good computers too, you could get a new Powerbook (this was pre MacBook) if you wanted. So, if you want one for school that sort of thing might be worth looking into.