Register Via HMRCs Website:

https://www.gov.uk/what-is-the-construction-industry-scheme

You will be notified of your UTR (Unique Taxpayer Reference) number that will identify you on HMRC’s system. You will need to give us your UTR number, using this, along with your name and National Insurance number, we will immediately verify you with HMRC.

Sub-contractors who are registered with a UTR number will be taxed at 20% on all income at source. By law sub-contractors not registered with a UTR number will have tax deducted at 30%.

How to register for NICs

You will be responsible for making your own National Insurance Contributions and will need to arrange to pay these by direct debit with HMRC. The NIC’s helpline number is 08459 15 46 55.

Alternatively you can go to the HMRC website to and complete the following form:

https://www.gov.uk/pay-class-2-national-insurance/direct-debit

You will be responsible for Class 2 NI, currently £3.15 per week. There may also be some Class 4 NI and tax applied to the profit element of your income once your tax return has been filed.
Please note: this does not apply to you if you are a CIS Umbrella PAYE customer.