Magento appears to support only GMT, without any visable option to select BST British Summer Time or set a GMT Offset within the Admin.
This seems to result in the Magento time being incorrect for half the year for all UK users.
Server time has no bearing, as Magento handles time independently.
This old thread raised the issue back in August 2008, over a year ago:
Having spent many hours examining code and searching the forum and google without success, has anyone managed to resolve this?