The 9th EC Directive on Summer Time, to be precise.
Here's the press release that I received yesterday from the Department for Business, Innovation & Skills
Summertime beginsSo now you know ...
Summer time will start on Sunday 28 March at 1.00am GMT throughout European Union Member States. The clocks go forward an hour. This means that at 1.00am (GMT) the UK will move to 2.00am British Summer Time (BST).
Notes to Editors
1. The 9th EC Directive on summer time harmonised, for an indefinite period, the dates on which summer time begins and ends across member states as the last Sundays in March and October respectively. Under the Directive, summer time begins and ends at 1.00am GMT in each Member State. Amendments to the Summer Time Act to implement the Directive came into force on 11 March 2002.
2. Time zones are the responsibility of individual Member States and vary across the EU. The UK is not planning to move to Central European Time.