The Britannian flag resembles the St. George's Cross, the flag of England, warped with the Union Flag of the United Kingdom. It bears a unique coat-of-arms. On the coat-of-arms, the lion represents royalty (or the Emperor) while the serpent represents "death and rebirth".
However, the arms of Britannia depicted on the flag are not correct in the heraldic sense. For example, in the arms the serpent's Vert (green) meets the field's Sable (black) - both Vert and Sable are colors and thus may only meet metal, such as Argent (silver/white) and Or (gold/yellow). A similar mistake is seen in the mantling - the green leaves or cloth around the arms. The rule has it that the color is - unless the opposite is specified - always on the outside and the metal on the inside, while two colors may never meet even in the mantling. The lack of a motto despite the existence of The closest attempt to blazoning the depicted coat of arms of Britannia would be:
"Sable a lion Or langued Gules and a serpent Vert langued Gules(or proper), both winged Argent , fighting and intertwined. Mantled Vert and Imperially crowned proper."