I've seen similar ranges advertised. It's probably worth noting that it's mostly the big financial firms that tend to offer this kind of money (£600+/day), and as well as the technical skills ig1 mentions, most positions also require real world experience working in their field. You are unlikely to jump from writing business admin software or games into financial modelling at that kind of money even if you've got a decade of programming experience and all the technical skills they can think of.

Also, keep in mind that these places are all based in London, so you have to factor in either relatively high accommodation costs or a significant amount of both time and money on the commute.

Also also, when you deal with these guys, you are usually not selling your services so much as your soul, because you aren't going to have much time and energy left to enjoy your off hours for as long as you're working there.

(I've been invited to work at these places but never taken them up on it, and having seen the effect it has had on some of my close friends, I have never regretted going a different way.)

Care to elaborate please? (FIX engine?)