On 30th March 2015 the Eurpoean Commission published a fact sheet on security measures in civil airliners. Included in this fact sheet is the following.
What are the current rules on the minimum crew members required in the cockpit?
On 27 March 2015, EASA (the European Air Safety Agency) has issued a recommendation for airlines to observe the “four-eye-rule” in the cockpit; stipulating that in the case of the Captain or First Officer leaving the cockpit, a member of the crew should be present in the cockpit with the remaining pilot.
European safety regulations require that pilots shall remain at the aircraft controls unless absence is necessary for physiological or operational safety needs.
There is no European requirement that a member of the cabin crew must enter the cockpit in the event a pilot needs to take a short break for such needs. There is however a requirement that the cockpit door can be opened from the outside in case of emergency.
The question is therefore as to why the cockpit door could not be opened from the outside in this instance.