GOV.UK
Register as an employer
You normally need to register as an employer with HM Revenue and Customs (HMRC) when you start employing staff, or using subcontractors for construction work.
You must register before the first payday. It can take up to 2 weeks. You can’t register more than 2 months before you start paying people.
You must register if you’re employing yourself, eg as the only director of a limited company.
Most new employers can register online. Find out whether you need to register and how to do it.