If you're a contractor under the Construction Industry Scheme (CIS) there are certain rules you'll need to follow. For example, you have to tell HM Revenue & Customs (HMRC) each month about all the payments you've made to your subcontractors within the scheme. You do this by making a monthly return.
To help HMRC check you're making your monthly returns correctly you're expected to keep records of your payments to subcontractors. You have to keep these records for a certain length of time so that HMRC can check them when it needs to.