I've got two sections of code which forces the forum to either add 1 hour or use GMT. I just comment out the section I don't want (so technically it's done manually, but no one on here would have noticed 😃 )
The server updates automatically.
//
//This section for GMT
//return ( !empty($translate) ) ? strtr(@gmdate($format, $gmepoch + (3600 * $tz)), $translate) : @gmdate($format, $gmepoch + (3600 * $tz));
//
//This section for BST
return ( !empty($translate) ) ? strtr(@gmdate($format, $gmepoch + (3600 * ($tz+1))), $translate) : @gmdate($format, $gmepoch + (3600 * ($tz+1)));
Running BST so top line is commented out using //