The Virgin Islands celebrate the feast of St Ursula annually on 22 October.
Christopher Columbus named the Virgin Islands in honour of the saint in 1493.
The British Antarctic Territory celebrates the Birthday of HM The King annually on 14 November.
The Falkland Islands celebrate the Birthday of HM The King annually on 14 November.
Alderney celebrates Homecoming Day annually on 15 December.
The people of Alderney were evacuated in June 1940 before the German occupation.
Homecoming Day marks the day the islanders could first return home in 1945.
The Pitcairn Islands celebrate Bounty Day annually on 23 January.
Bounty Day commemorates the burning of HMS Bounty by the mutineers in 1790.
The start of LGBT+ History Month 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 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 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 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.
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/