In any case make sure you first read the how to fill your tax return pdf for that tax year it s on the same hmrc page. Hmrc was formed by the merger of the inland revenue and. Her majesty s revenue and customs hm revenue and customs or hmrc is a non ministerial department of the uk government responsible for the collection of taxes the payment of some forms of state support and the administration of other regulatory regimes including the national minimum wage and the issuance of national insurance numbers.