Unfortunately, agencies stopped paying their CIS workers direct many moons ago, though they will still pay other workers direct.
Their excuse at the time was IR35.
Instead of being paid by the agency, you will have to sign up with and be paid through a payroll company owned by the agency.
The payroll company will charge you a fee to process your payment.
So the agencies get paid by the client to supply you, and then get paid by you to be supplied.
If you have a Ltd. Co. then you should be able to be paid direct CIS from the agency, though many are now insisting you get paid through a payroll company
If you get paid direct, this will increase your earnings anything from £18 - £30 per week.
With CIS, you will have 20% of your earnings deducted at source.
You will then have to complete a Self Assessment at the end of the year, where you can claim any allowable expenses, pay your NI and claim back any tax owed.
If being paid through a payroll company, you will have the 20% tax deducted after the fee has been taken.
Umbrella is a complete scam.
You are paid as if you are an employee but no one employs you.
The payroll company charges you a fee, then deducts Tax, NI and Employer’s NI contribution from your money.
They are no longer allowed by HMRC to allow for any expenses incurred.
You will then have to file a Self Assessment to claim back the tax and NI owed on any expenses you have incurred.
Not sure what (if anything) would happen to any overpaid Employer’s NI contributions.