FO left the cockpit and FA entered as per SOP's.
When the FO tried to re enter the door refused to unlock.
On board engineer, FO, FA and Capt tried to open the door for a l o n g time with in accordance with all procedures with no success. After around 350 miles Capt finally was able to kick in the bottom panel just prior to TOD.
Just another day in the life a pilot with Poxie style maintenance.