Since 2002 the European Union (E.U.) summer time rule has been standardized and implemented from
the last Sunday in March to the last Sunday in October. The duration of
Summer Time varies between 210 days (30 weeks) in some years and 217 days (31 weeks) in others. On transition either way, the clocks in all time zones change simultaneously at 01:00 UTC.
Ref:
Directive 2000/84/EC of the European Parliament and of the Council of 19 January 2001 on summer-time arrangements
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:32000L0084:EN:HTML