UK Government guidelines state that the Union Flag should be flown on Remembrance Sunday (the second Sunday in November).
https://www.gov.uk/guidance/designated-days-for-union-flag-flying
Scottish government guidance also lists Remembrance Sunday as a flag flying day.
The Union Flag is specified.
https://www.gov.scot/publications/flag-flying-on-government-buildings/
The Royal British Legion recommends flying the Union Flag on Remembrance Day (11 November) and Remembrance Sunday.
https://support.britishlegion.org.uk/app/answers/detail/a_id/263/~/remembrance-faqs
The flag should not be flown at half mast on either day.
Lancashire Day has taken place annually on 27 November since 1996.
It commemorates the day when Lancashire first sent representatives to Parliament, the Model Parliament of King Edward I (1295).
Bedfordshire Day takes place annually on 28 November.
The date, chosen by popular vote, commemorates the birthday of John Bunyan.
Several alternative options included:19 January – earldom (later dukedom) of Bedford recreated (1550); 12 April – Bedfordshire County Council granted its coat-of-arms (1951); 20 June – siege of Bedford Castle begins (1224); 13 August – Blenheim Day, celebrated by the Bedfordshire Regiment and its successors; 12 September – birth of prison reformer John Howard (1726); 14 October – first flight of the airship R101 from Cardington (1929); 6 November – 1st and 2nd Battalions Bedfordshire Regiment meet at Bailleul en route to Ypres (1914); 15 November – first High Sheriff of Bedfordshire appointed (1575); 25 November – feast of St Catherine, patron saint of spinners, weavers and lacemakers; 15 December – birth of Olympic athlete Harold Abrahams (1899).
Caernarfonshire Day takes place annually on 28 November.
It commemorates the death of Prince Owain Gwynedd, King of Gwynedd (1137–70).
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.
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 Patrick’s Day is listed as a flag flying day (for Northern Ireland only) by UK government guidance.
The Union Flag is specified.
https://www.gov.uk/guidance/designated-days-for-union-flag-flying
There is no official, current pan-Ireland or Northern Ireland flag that may be used to mark St Patrick’s Day.
St Patrick’s Saltire is one of several possible alternatives.
St Cuthbert (c.634–87), prior of Lindisfarne, is buried in Durham Cathedral.