Shropshire Day takes place annually on 23 February, the feast of St Milburga.
Milburga (d.715) was a Mercian princess and the abbess of Wenlock Priory.
In the eleventh century, her reputation as a miracle worker turned Much Wenlock into a place of pilgrimage.
Visitors flocked to St Milburga’s Well seeking cures for their ailments.
St David’s Day is Wales’ national day.
The Senedd Cymru flies the Welsh national flag – Y Ddraig Goch (The Red Dragon) – all year round.
On St David’s Day it also flies the flag of St David (below).
https://senedd.wales/media/hl5dtuct/foi-574-final-redacted-response-saes.pdf
St David’s Day is also listed as a flag flying day (for Wales only) by UK government guidance.
The Union Flag is specified.
https://www.gov.uk/guidance/designated-days-for-union-flag-flying
St Piran, the patron saint of tin miners, is one of Cornwall’s patron saints.
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/
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 George’s Day is England’s national day – St George was named as England’s principal patron saint in 1416.
St George’s Day is listed as a flag flying day (for England only) by UK government guidance.
https://www.gov.uk/guidance/designated-days-for-union-flag-flying
The Union Flag is specified.
Oliver Cromwell (1599–1658) was an English statesman, politician and soldier.
He was MP for his native Huntingdon (1628-9).