HM Revenue & Customs (HMRC) is the tax authority of the UK government.
HMRC collects all direct and indirect taxes in the UK, such as including income tax, corporation tax, and VAT, as well as managing Statutory Payments such as statutory sick pay and statutory maternity pay, and helping families and individuals with financial support through payment of tax credits.
When you’re self-employed, you’ll be dealing with HMRC on a regular basis, through your Self Assessment and other enquiries.
They have a useful helpline for self-assessment questions, which you can call on 0300 200 3310.