Union dispute

Pedants suffered a blow as the chief vexillologist of the Flag Institute declared that the Union Jack and Union Flag are interchangeable terms, the latter being just as correct on land as it is at sea. Here are both sides of the argument:

evidence for ‘union jack’
being correct only at sea

— A ‘jack’ is an old term for the bow flag of a vessel, and was in use before the Union Jack came into being.