Your comparing permanent and self employed temporary jobs. Contracting jobs pay a lot more, even for juniors. They're paying for the ability to easily get rid o

Your comparing permanent and self employed temporary jobs. Contracting jobs pay a lot more, even for juniors. They're paying for the ability to easily get rid of you, paying no employee crap(NI, etc) etc So it is justified. 400 GBP is low end dev. Companies such as Accenture rent out juniors for a lot more than that.