|>>|| No. 12121
Actually, a big part of the price premium is to do with the funding model.
As a member of permanent staff, your post is funded from the trust's operational budget, which means it's subject to the stresses of below-inflation increases (i.e. real-terms cuts), and the resulting pressure on the trust to identify what they do best and find more ways of doing less of it better. If they need an extra nurse but there's no headroom in the operational budget, they can't create the post.
As agency staff are effectively either at-will or for a fixed term, the accountants can do a bit of voodoo and charge them to capital budgets. If they need an extra nurse but don't have the funding to create a post, they can spend money from other budgets on agency and contract staff.
The agencies know that they are providers of last resort, so can gouge to fuck. They also know that if they can poach staff away from payroll, that directly increases demand for their services. That means an agency can effectively take an NHS employee away from and hire them back to the same trust at a premium. In order to be able to attract staff, knowing they aren't offering the same benefits they have to offer significantly higher pay, otherwise nobody would join them.
tl;dr fatcats gonna fat.