This article concerns the ensigns flown by vessels and aircraft of the United Kingdom and its overseas territories, and by certain nations of the Commonwealth.
A British ensign in British maritime law and custom, is the identifying flag flown to designate a British ship, either military or civilian. Such flags display the United Kingdom Union Flag in the canton (the upper corner next the staff), with either a red, white or blue field, dependent on whether the vessel is civilian, naval, or in a special category. These are known as the red, white, and blue ensigns respectively.
Outside the nautical sphere, ensigns are used to designate many other military units, government departments and administrative divisions. These flags are modelled on the red, white, and blue naval ensigns, but may use different colours for the field, and be "defaced" by the addition of a badge or symbol, for example the sky blue with concentric red, white and blue circles of the Royal Air Force ensign.
Today's white ensign, as used by Royal Navy ships, incorporates the St George's Cross (St George's Ensign). British yachts owned by members of the Royal Yacht Squadron are authorised to apply for a permit to wear this ensign. Defaced white ensigns include that of the British Antarctic Territory.
The Union Flag (also known as the Union Jack) should only be flown as a jack by Royal Navy ships when moored, at anchor, while underway and dressed with masthead ensigns or if the Monarch or an Admiral of the Fleet is on board. The Union Flag may also signal that a court martial is in progress.
The use of the Union Flag as an ensign on a civilian craft is still illegal. ever since Charles I ordered it be restricted to His Majesty's ships "upon pain of Our high displeasure" in the 17th century, mainly due to its unauthorised use by merchant mariners to avoid paying harbour duties by passing themselves off as Royal vessels.
Modern usage 
British ensigns currently in use can be classified into five categories, in descending order of exclusivity:
- the White Ensign
- the Blue Ensign
- the Blue Ensign defaced
- the Red Ensign defaced
- the Red Ensign
The traditional order of seniority was red, white and blue, with the red as the senior ensign.
Since the reorganisation of the Royal Navy in 1864, use of the White Ensign (a red St George's Cross on a white field with the Union Flag in the canton) has been restricted to ships, boats, submarines and on-shore establishments of the Royal Navy. The Royal Yacht Squadron also fly the white ensign by special dispensation.
The Blue Ensign (dark blue field with the Union Flag in the canton) undefaced is worn by masters of vessels in possession of a warrant issued by the Director of Naval Reserves, and by the members of certain yacht clubs. Such warrants are issued to officers in the active or retired lists of the Royal Naval Reserve and the maritime reserve forces of other Commonwealth Realms and territories. The master must be of the rank of lieutenant RN or above, and fishing vessels must be crewed by at least four other Royal Naval reservists or pensioners. The Ensign of the Sea Cadet Corps is a blue ensign defaced by the SCC badge. Under the terms of a Memorandum of Understanding with the Ministry of Defence, officers of the Sea Cadet Corps hold their ranks as (SCC) RNR on a 'nominal honorific' basis, and are included on the Navy List as a courtesy (though they are not commissioned, but 'appointed' within the Corps).
Royal Fleet Auxiliary Ensign
Ensign of the defunct Royal Maritime Auxiliary Service
Royal Engineers Ensign
Royal Logistic Corps Ensign for vessels commanded by a Commissioned Officer
Royal Logistic Corps Ensign for vessels commanded by a Non-Commissioned Officer
Ensign of the Sea Cadet Corps
Ensign of the Northern Lighthouse Board
British government departments use a variety of blue ensigns defaced in the fly with the department badge, and colonial governments use blue ensigns defaced with the colonial badge. Other defaced ensigns were used by vessels of the Mersey Docks and Harbour Board, the Humber Conservancy, Custom House, the Board of Trade, Lloyds of London, the Post Office, cable laying ships, and other departments including War Office Ordnance. The flag of Australia and those of its states as well as the flag of New Zealand are defaced blue ensigns. Several yacht clubs are also entitled to fly blue ensigns defaced by their club badge.
The Red Ensign (red field with the Union Flag in the canton) defaced by a badge is flown by Trinity House and various organisations and yacht clubs. Merchant ships and private vessels registered in British colonies and dependencies, and in several Commonwealth realms, fly the Red Ensign defaced by the badge of their territory.
The Red Ensign undefaced is for the use of all other British merchant navy ships and private craft. The Red Ensign is the correct flag to be worn as courtesy flag by foreign private vessels in United Kingdom waters. Merchant vessels from British overseas territories and Crown dependencies are entitled to red ensigns defaced with the badge of their territory.
Other ensigns 
British Civil Air Ensign in use at Hunsdon Airfield.
Ensign of the Air Training Corps
Ensign of the Royal Observer Corps
The flag of the British East India Company, like the Cambridge or Grand Union Flag of the American colonies, had a red and white striped field. There were similar red-and-white and green-and-white striped ensigns in the English Navy in the 16th century. Similarly in flag plates from the 17th and 18th centuries there are representations of the Guinea Jack of the Royal Africa Company in various forms; the jack consisted of a St George's Cross within a double border of red and white chequers. The flag of Hawaii is a British ensign with a background of white, red and blue stripes.
Also in existence is a Royal Air Force (RAF) ensign and a civil air ensign, both of which have a sky blue field, with the Union Flag in the canton. The RAF Ensign is defaced with the red-white-blue RAF roundel, while the field of the civil air ensign is charged with a large dark blue cross fimbriated white. The flag of Tuvalu and that of Fiji are also defaced sky blue ensigns.
The white ensign of the Commissioner of the Northern Lighthouse Board is unique in that it remains the only example of a pre-1801 Union Flag in official use today. This flag is only flown from vessels with Commissioners aboard.
There are two "yellow" ensigns in use in the South Pacific, both featuring the Southern Cross. The personal flag of the Governor of Victoria, Australia, has been the flag of Victoria with a yellow instead of a dark blue background. The flag of Niue, a self-governing dependency of New Zealand, is also a yellow ensign. More unusually, it is the Union Flag canton rather than the fly which is defaced with a modified Southern Cross.
There is some evidence of the existence of a Green Ensign in British Ireland, defaced with a gold Irish harp in the fly. It is not clear to what extent this unofficial ensign was ever in use by Irish merchant ships at the time.
The Royal Hospital School 
The Royal Hospital School is the only independent school in the United Kingdom to have been continuously awarded the "Queens Banner" and its own distinctive school ensign.
Prior to 1864, red, white, and blue were the colours of the three squadrons of the Royal Navy, which were created as a result of the reorganisation of the navy in 1652 by Admiral Robert Blake. Each squadron flew one of the three ensigns. In addition to the Admiral of the Fleet (who was Admiral of the Red), each squadron had its own admirals, vice admirals and rear admirals, e.g. Lord Nelson was Vice Admiral of the White at time of death.
The red squadron tended to patrol the Caribbean and north Atlantic, the white the coasts of Britain, France and the Mediterranean, while the blue patrolled the south Atlantic, Pacific and Indian oceans. The flags of the various former British colonies often have grounds of the same colour as their protective squadron. Hence Bermuda has a red ground and Australia and New Zealand blue. Canada's flag was a red ensign from founding until the adoption of the more familiar maple leaf flag in 1965.
The flag of the United States also follows this pattern; early flags of the American Revolution were modified Red Ensigns. The Grand Union Flag added six white stripes to the Red Ensign; this flag was used during the fight for independence until the Union Flag in the corner was replaced by the current stars in 1777.
Reference was sometimes made to "the yellow squadron". This squadron did not actually exist but was a term used unofficially to describe those naval personnel who worked ashore or did not have a ship. Therefore there was no 'Yellow ensign'.
Canadian ensigns 
In 1868, the British Admiralty made the Canadian Blue Ensign the proper flag for ships of the Canadian government, and in 1892, the Admiralty approved the use of the Canadian Red Ensign by Canadian merchant ships.
From about 1870, Canada unofficially used a Red Ensign with the arms of its provinces on one shield as its national flag (the Canadian Red Ensign). In 1924, an order-in-council made the flag official (for certain purposes) and replaced the provincial arms with the royal arms of Canada. The red ensign was replaced by the current red and white maple-leaf flag in 1965. In that same year, the provinces of Ontario and Manitoba adopted red ensigns defaced by their provincial arms as their provincial flags. (see Flag of Ontario and Flag of Manitoba)
See also 
- Blue Ensign
- Red Ensign
- Green Ensign
- Lists of flags
- Maritime flag
- Union Flag
- Flags based on British ensigns
- Flag of Australia
- Flag of Canada
- Flag of New Zealand
- Flag of Tuvalu
- List of Canadian provincial and territorial symbols
- "Merchant Shipping Act 1995". Retrieved June 05, 2012.
- "Northern Lighthouse Commissioner's Flag". Flags of the World. Retrieved 20 February 2010.
- Flags and flag etiquette. In Fowler, Jean (Ed.): Reed's Nautical Almanac 1992, pp. 13:1–13:8. East Molesey: Thomas Reed Publications. ISBN 0-947637-96-6