In general continuous lights are not very good for photography. Working indoors you want your lights to overpower any ambient light in the room so you don't end up with a mixture of tungsten or florescent light with whatever color temperature your lights are. You also would like enough light to use ISO 100, f/8 or f/11. If you get continuous lights that are that bright, they are going to be hot and make your subject squint. You will have trouble getting portraits with nice looking eyes in them.
For photographing portraits you generally need flash or strobes. You can take portraits with your 580EX II flash in a medium softbox or umbrella and a reflector to provide fill. This won't get you to ISO 100 f/11, but you could probably do f/5.6 or increase the ISO for more depth of field. This setup would be inexpensive, but the white background paper is not going to look "white". To get white background paper to look really white, you have to use a minimum of 2 lights on the background, and 4 would be better.
There are some inexpensive strobe kits available in the US. With the white paper background you probably need at least 4 strobes. One for key, one for fill, and 2 for the white paper background. I have no idea what is available in the UK, so I cannot comment on specific brands.