The Accession Day of HM The King is listed as a flag flying day by UK government guidance.
The Union Flag is specified.
The Accession Day of HM The King is also listed as a flag flying day by Scottish government guidance.
The Scottish Saltire is specified.
Gibraltar celebrates its National Day – first held in 1992 – annually on 10 September.
The date marks Gibraltar’s first sovereignty referendum (1967), when voters chose to stay under UK sovereignty rather than transfer to Spanish sovereignty.
Rutland Day takes place annually on 13 September.
It marks the defeat of the ‘Grand Assault’ during the siege of Gibraltar in 1782.
Among the defenders were the men of the 58th (Rutlandshire) Regiment of Foot.
Gloucestershire Day was first celebrated in 2020.
Derbyshire Day takes place annually on 22 September.
BBC Radio Derby presenter Andy Whittaker organised a vote, and the chosen date commemorates the first raising of the flag.
Alternative suggestions included: 28 July – Derby, the county town, granted city status; 12 May – the birthday of Florence Nightingale, who spent her early years in the county.
Cumberland Day takes place each year on 24 September.
It marks the anniversary of the baptism of renowned local character John Peel (1776-1854).
Montmouthshire Day takes place each year on 25 September, the feast of Saint Cadoc or Cadog (born c. 497).
Cadoc was the founder of the monastery of Llancarfan, and a pioneer of Celtic Christianity in Wales.
Westmorland Day takes place annually on 29 September.
It marks the date in 1397, when King Richard II created Ralph Neville the first Earl of Westmorland.
A poll at the Westmorland County Show (2013) chose this day.
Other options included: 30 January – birth of Lady Anne Clifford; 30 July – death of Thomas de Strickland; 1 October – battle of Tinghai; 21 October – death of Earl Ralph Neville; 18 December – battle of Clifton (perhaps the last battle on English soil).
Lincolnshire Day takes place annually on 1 October.
It commemorates the Lincolnshire Rising, which began at Louth on 1 October 1536.
The rebels were protesting against the English Reformation and the Dissolution of the Monasteries.