[en] The commissioning of nine Magnox and two Advanced Gas-cooled Reactor Nuclear Power Plants in the United Kingdom during the last sixteen years under the regulatory control of the Nuclear Installations Inspectorate of the Health and Safety Executive has been based on a Stage Approval Philosophy starting with proof-testing of the primary gas circuit and concluding with tests on the reactor at full power. The practical experience gained during this period has enabled the Nuclear Installations Inspectorate to rationalize the procedures and test requirements without compromising safety standards. The Operating Rules and Maintenance Schedules are approved for commissioning and during this period are reviewed for their adequacy for future power operation of the plant. The organization, documentation, test procedures and the commissioning programme used for the Advanced Gas-cooled Reactors are briefly explained