I wrote a lot about cheap lighting in the guide at the top of this section. A nice system for you might be to start off with compact fluorescents. Get at least 26 watts, and try and get one per plant. You can add more later if you want. Try and get them with a bluer spectrum if possible, this makes your plants grow greener and less spindly. Anyway, while you're vegetating your plants, try and save up for a high-pressure sodium light, probably a 250-watt or 400-watt model.

I have no idea what one of these lights costs in the UK, or where someone would get one, but a HPS light will pay for itself in improved yields, and you're best off getting one.

With fluorescent lights for vegetation and HPS for flowering, you can have two crops going at once, which will also give you more bud.