Gwydyr House is one of the few public buildings in Whitehall not flying St George's flag today.
The BBC reports that all UK government buildings with two flag poles are being encouraged to fly the English national flag, alongside the union flag, on St George's Day.
The Wales Office is apparently exempt from the rule and is flying the union flag and the red dragon.
Downing Street says it will be flying the Welsh national flag on March 1 next year. No word yet on whether those Whitehall departments flying the flag of St George will follow suit on St David's Day.