The forum default is set to Greenwich meantime with BST enabled. This shows correctly as set for any guest visitors.
It is up to individual members, when logged in, to set the date and time to their personal requirements so as to accommodate members from differing time zones.
For UK members go to User Control Panel/Board Preferences/Edit Global Settings/Summer Time/DST is in effect: select "yes". Then submit.
For non UK members select the appropriate time zone from the drop down menu.