When running on Windows, PHP’s timezones don’t always play nicely with the Windows implementation of daylight savings time (DST). The code below is an easy workaround to this; simple use date("I") to work out if it is summer or not and combine this with date() and strtotime() to get the spot-on time including your GMT offset.
For the UK the DST offset is 1 hour, so the following works perfectly:
date('Y-m-d H:i:s',strtotime('-' . date("I") . 'hours'))
