Under the Construction Industry Scheme (CIS), contractors deduct money from a subcontractor’s payments and pass it to HM Revenue and Customs (HMRC).
The deductions count as advance payments towards the subcontractor’s tax and National Insurance.
Contractors must register for the scheme. Subcontractors don’t have to register, but deductions are taken from their payments at a higher rate if they’re not registered.
HMRC make it easy to join CIS but its hard to find the instructions on how to leave or cancel CIS.
For those who have struggled to find the instructions here they are
If you stop trading or using subcontractors
stop filing monthly CIS reports
Do this even if you’ve stopped using subcontractors temporarily, for example because you’re using your own employees to carry out work.
In general I find a letter works best as you can send it recorded delivery and prove it was sent, you write to this address
National Insurance Contributions and Employers Office
HM Revenue and Customs