With the nights drawing in, clocks go back an hour as British Summer Time (BST) officially draws to a close. British Summer Time starts on the last Sunday in March (27th March in 2011) and ends on the last Sunday in October (today).
The clocks go forward precisely at 1am Greenwich Mean Time (GMT) to 2am BST. We effectively "lose" an hour.
Today, we "gain" an hour when the clocks go back at 2am BST and the UK moves to 1am GMT.
It helps to remember that clocks spring forward in Spring and fall back in Fall (North American word for Autumn)