St Felix (d.647/8), the first bishop of the East Angles, introduced Christianity to the kingdom.
The birthday of the Duke of Edinburgh (and Earl of Forfar) is an official flag flying day only in Scotland, not in the rest of the UK.
https://www.gov.scot/publications/flag-flying-on-government-buildings/
Commonwealth Day is the second Monday in March.
The UK government states that the Union Flag should be flown.
https://www.gov.uk/guidance/designated-days-for-union-flag-flying
The Scottish government states that the Commonwealth flag should be flown.
https://www.gov.scot/publications/flag-flying-on-government-buildings/
The Senedd Cymru states that the Commonwealth flag should be flown.
https://senedd.wales/media/hl5dtuct/foi-574-final-redacted-response-saes.pdf
St Cuthbert (c.634–87), prior of Lindisfarne, is buried in Durham Cathedral.
West Riding Day marks the anniversary of the battle of Towton (1461), reputedly the largest and bloodiest battle ever fought on English soil.
The Yorkist forces defeated the Lancastians, leading to a change of royal dynasty.
Edward Duke of York deposed King Henry VI (ruled 1422–61, 1470–1) and took the crown as King Edward IV (ruled 1461–1470, 1471–83).
The first Cheshire Day took place in 2021.
It commemorates the date when King Edward I, who was also Earl of Chester, reconfirmed a charter of liberties for the county.
St Magnus, then Magnus Erlendsson, was Earl of Orkney (1106–c.1117).
He was sanctified in 1136.
Oliver Cromwell (1599–1658) was an English statesman, politician and soldier.
He was MP for his native Huntingdon (1628-9).
International Workers’ Memorial Day is a day of remembrance and action for workers killed, disabled, injured, or made unwell by their work.
It is an official flag flying day only in Scotland, not in the rest of the UK.
The saltire(s) should be hoisted right up and then lowered to half-mast for the day.
https://www.gov.scot/publications/flag-flying-on-government-buildings/
Staffordshire Day commemorates the foundation date of Josiah Wedgwood and Sons (1759).
The date was selected by public vote from a list that includes: 5 July – discovery of the Staffordshire Hoard (2009); 6 September – the future King Charles II hid in an oak tree in South Staffordshire (1651); 18 September – Doctor Samuel Johnson born in Lichfield (1709); 27 September – James Brindley, renowned engineer and resident of Leek, died (1772)