franktouch:
To be honest its not a con, there’s a demand for it more on the agencies side as they don’t want workers on their book for many reasons.But if you are putting in expenses worth £50 a week then you will be better off than just being on the agencies PAYE.
THIS is one of the reasons that HMRC is cracking down on the whole umbrella scheme scams. If you are on an umbrella scheme you are NOT self employed and therefore limited in what you can actually legally claim for. I had one of these ‘schemes’ trying to tell me I could claim expenses of up to £150 WEEK, as I would be working nights. 
Unless you are genuinely self employed through your own limited company, then you are still someone’s employee, irrespective of what some idiot agency ‘consultant’ might try to claim to the contrary. As to why anyone would be willing to pay someone to process their own payroll when still legally a PAYE employee, still remains a complete mystery to the rest of us. 