BST and GMT
In the UK the clocks change to British Summer Time (BST) and Greenwich Mean Time (GMT) at 01:00 hours GMT on the last Sunday of March and October repectively.
When the change to BST occurs your clock will show 01:00 and so you should move it forward one hour to 02:00 making clock time appear to progresses as...
00:59:58
00:59:59
02:00:00
02:00:01
...which looks like 01:00:00 to 01:59:59 just don't occur!
Moving from GMT to BST has the effect of loosing one hour of sleep for most people.
When the change to GMT occurs your clock will show 02:00 and so you should move it backward one hour to 01:00 making clock time appear to progress as...
01:59:58
01:59:59
01:00:00
01:00:01
...which looks like 01:00:00 to 01:59:59 occur twice that night but 02:00:00 occur's just once!
Moving from BST to GMT has the effect of gaining one hour of sleep, or an extra hour awake, for most people.
British Summer Times
In 2007: the Sundays of 25 March and 28 October
In 2008: the Sundays of 30 March and 26 October
In 2009: the Sundays of 29 March and 25 October
In 2010: the Sundays of 28 March and 31 October
In 2011: the Sundays of 27 March and 30 October
All changes from GMT to BST and BST to GMT occur at 01:00:00 GMT