In 1801, the Cross of St. Patrick was added to the flag when Ireland joined the Union. This cross was placed with the Cross of St. Andrew. While Ireland's south broke away from the Union in 1921, the flag remains the same. The 1801 Union Flag, popularly known as the Union Jack, was introduced by Royal Proclamation, as a royal banner to be "displayed on all His Majesty's Forts and Castles, and also on board all His Majesty's Ships of War."

In 1801, the Act of Union united the Kingdoms of Great Britain and Ireland and King George III dropped the ancient claim to the French throne. The new royal standard was quartered with the English Royal Crest (crowned Lion Passant Guardant on a Royal Crown) in the 1st and 4th quarter, the Royal Standard of Scotland in the 2nd quarter and the Irish harp in the 3rd quarter. For the Electorate of Hanover, there was an shield with a Elector's hat above it added in the center.

The so-called "Pilot Jack," sometimes called the United Kingdom's Civil Jack, was originally formally established in 1823 as a signal flag to indicate that a pilot was required, and needed on-board a ship in harbor. Pilots are often required in restricted waterways where there are congested waters or navigational hazards such as harbors or river mouths. Since the law establishing it did not stipulate that it could not be also flown at sea, the convention started for merchant ships to use the jack at sea when under way as a sort of unofficial national flag.

The accession of Queen Victoria ended the personal union between the United Kingdom and Hanover and the center shield and crown were removed. The flag was quartered with the English Royal Crest (crowned Lion Passant Guardant on a Royal Crown) in the 1st and 4th quarter, the Royal Standard of Scotland in the 2nd quarter and the Irish harp in the 3rd quarter. The Harp of the Kingdom of Ireland remained the same despite Ireland splitting into the Northern Ireland and the Republic of Ireland in 1921. Wales doesn't get the 4th quarter because Wales is considered a principality, not a kingdom (much to the frustration of some Welsh patriots). This coat-of-arms has remained unchanged since 1837.

In 1869, governors of colonies, military authorities, diplomatic officers and consular agents were first assigned a defaced Union Jack for their use when they sailed on a sea going vessel, but on land it remained a plain Union Jack. In 1940, this was changed, so that the defaced ensigns were approved for use at Government Houses from sunrise to sunset. The flags were official describe as an "Union Flag with approved arms or badge of the colony, emblazoned in the centre thereof on a white ground surrounded by a green garland."

St. Edwards Crown version (1953-1999)		St. Edwards Crown version (after 1999)

The crown used at the center of the Consular Officer flag has been changed twice from the original Tudor Crown. First, in 1953 it was changed to a St. Edwards Crown, then in 1999, the St. Edwards Crown was re-drawn with the white circle being outlined in black. Since 1869, the British Consular Flag Afloat has been the royal arms applied directly (no white disc as used for diplomatic officers on the Union Flag) to the field of a Blue Ensign and remains unchanged.

The Royal Navy had, since the late 1620s/early 1630s, been organized into three squadrons, which flew either red, white or blue ensigns with a Saint George's cross canton. In 1707, a Union canton replaced the Saint George's canton on the ensigns, and the Red Ensign remained not only the ensign of the senior and most numerous squadron in the Royal Navy, but also the ensign which all merchant ships were ordered to fly. The British still use three basic maritime ensigns today. However, the practice of adding shields to the flies for overseas territories and Commonwealth member nations to the red or blue versions increases the possible versions. The ensigns are/were used not only for territories, but also government departments and some yacht clubs. Currently there are over 133 defaced ensigns in use, plus an additional 68 being used for yacht clubs. Add to this another 99 obsolete ensigns from the British Isles, 52 additional obsolete yacht clubs, and 303 obsolete ensigns from the Commonwealth and the Empire, and you have a staggering number of defaced ensigns now or once being used.

Trinity House (1514) is the general lighthouse authority for England, Wales, Channel Islands and Gibraltar, and responsible for pilotage throughout the United Kingdom. Until 1864 vessels in the service of certain United Kingdom public offices used defaced the red ensign with the badge of their office. In that year they were directed to transfer the badge to a blue ensign. For some reason Trinity House didn't do it and still have their badge of four Elizabethan ships quartered on a rectangular panel on a red ensign.

The Northern Lights is the general lighthouse authority in Scotland and the Isle of Man. The NLH ensign is a normal blue ensign with a white stylized lighthouse on the fly.

NLH Ensign 1786		NLH Commissioner's Flag 1786

The more slender lighthouse on the older versions of the NLH flag are of the lighthouse on Bell Rock in Scotland.

NLH Pennant 1786		NLH Pennant 1855

A square version of their blue ensign (both 1786 and 1855 styles) was authorized for use by Northern Lighthouse vessels as a jack.

Dare we say, "Long may it wave?"

A whole series of variant lighthouse drawings on NLH ensigns have been reported at various times as demonstrated on this whimsical elongated illustration by vexillologist Peter Hans van den Muijzenberg.

The Mersey Docks and Harbour Company (MDHC), formerly the Mersey Docks and Harbour Board (MDHB), now owns and administers the dock facilities of the Port of Liverpool, on the River Mersey, England. The Liverpool Town Council was the original port authority. As the port expanded and its management became more complex its affairs were delegated to a harbor board whose chairperson was usually a Royal Navy Officer.

The Board of Ordnance was originally created by Henry VIII in 1544 to supply guns, ammunition, stores and equipment to the King's Navy. The Great Master of Ordnance ranked immediately below the Lord High Admiral. By 1683, the Board had became a Civil Department of State, under a Master General, whose duties included supplying ordnance to the Army. It had a badge bearing three field guns in pale, and three cannon balls in chief was adopted as the Seal of the Board. This seal was used as the badge on the Red Jack of all Ordnance Board vessels.

The War Department was the United Kingdom government department responsible for the supply of equipment to the armed forces of the United Kingdom and the pursuance of military activity. In 1857, it became the War Office. Within the War Office the name "War Department" remained in use to describe the military transport services of the War Department Fleet and the War Department Railways.