From Wednesday HMRC will apply the same set of tax rules across PAYE, VAT, income tax, capital gains tax and corporation tax.
Changes include a new two-tier system of tax tribunals replacing General Commissioners, Special Commissioners and the VAT and Duties Tribunal.
HMRC is also simplifying the entry and leaving rules for small businesses using the VAT flat rate scheme.
From April 6 employers with 50 or more employers will have to file their employee starter and leaver notifications and similar pensions notifications online, and a new A4 version of the P45 form will replace the old style A5 form.
Changes have also been made to the P46 form.
HMRC permanent secretary for tax Dave Hartnett says: “These are important measures which will make it easier for businesses and their advisers to meet their obligations whilst making it easier to work with us and to get decisions on points of law. These initiatives will provide businesses with more consistency, certainty and faster on-line processing of key documents”.