St George's Cross in the context of "Flag of the United Kingdom"

The Blue Ensign is a British ensign that may be used on vessels by certain authorised yacht clubs, Royal Research Ships and British merchant vessels whose master holds a commission in the Royal Naval Reserve or has otherwise been issued a warrant. Defaced versions with a badge or other emblem are used more broadly; in the United Kingdom by authorised government or private bodies; and internationally by nations or organisations previously a part of the British Empire.

The evolution of the Blue Ensign followed that of the Union Jack. The ensign originated in the 17th century with the St George's Cross (the Flag of England) in the canton, and with a blue field.

The White Ensign, at one time called the St George's Ensign because of the simultaneous existence of a crossless version of the flag, is an ensign worn on British Royal Navy ships and shore establishments. It consists of a red St George's Cross on a white field, identical to the flag of England except with the Union Flag in the upper canton.

The White Ensign is also worn by yachts of members of the Royal Yacht Squadron and by ships of Trinity House escorting the reigning monarch.