At 2.00 am BST (1.00 am GMT) on Sunday 25 October 2009 UK clocks will move back by an hour as civil time moves from British Summer Time (BST) to Coordinated Universal Time (almost identical to Greenwich Mean Time).

Or, to put it more practically, UK residents can all look forward to their annual extra hour in bed on the last Sunday in October.

The Ninth European Parliament and Council Directive on Summer Time Arrangements states that summer (or daylight saving) time will be kept between the last Sunday in March to the last Sunday in October, and the changes take place at 01.00 GMT.

Find out more about daylight saving time in the Royal Observatory's fact file.