HM Revenue & Customs (HMRC) treat profits from UK land or property for tax purposes, as arising from a business. But for National Insurance contributions (NICs) purposes, to be classed as a self-employed earner, you need to show that the level of activities you carry out amount to running a business as opposed to simply carrying out the duties of a landlord.
As you have you've told HMRC that you're in land and property, we'll register you for Self Assessment. When you fill in your return, fill in additional sections known as supplementary pages.
Follow the link below for more information about the supplementary pages. https://www.gov.uk/self-assessment-forms-and-helpsheets. For National Insurance purposes, HMRC will send you a bill once a year to pay Class 2 NICs voluntarily.