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.
Europe Day is celebrated annually on 5 May and 9 May.
The Council of Europe designates 5 May, the anniversary of the Council’s founding.
https://www.coe.int/en/web/portal/5-may-europe-day
The European Union designates 9 May, the anniversary of the Schuman Declaration (1950).
https://european-union.europa.eu/principles-countries-history/symbols/europe-day_en
Neither date is listed as a flag flying day by UK government guidance, although the UK remains a member of the Council of Europe.
https://www.gov.uk/guidance/designated-days-for-union-flag-flying
Europe Day is listed on 9 May as a flag flying day by Scottish government guidance.
The European Flag is specified.
https://www.gov.scot/publications/flag-flying-on-government-buildings/
The Coronation Day of HM The King is listed as a flag flying day by UK government guidance.
The Union Flag is specified.
https://www.gov.uk/guidance/designated-days-for-union-flag-flying
The Coronation Day of HM The King is also listed as a flag flying day by Scottish government guidance.
The Scottish Saltire is specified.
https://www.gov.scot/publications/flag-flying-on-government-buildings/
Guernsey celebrates Liberation Day (Lé Jour dé la Libératiaon in Guernsey French) annually on 9 May.
The date commemorates the island’s liberation in 1945 from German occupation during the Second World War.
Jersey celebrates Liberation Day (Jour d’la Libéthâtion in Jersey French) annually on 9 May.
The date commemorates the island’s liberation in 1945 from German occupation during the Second World War.
Sark celebrates Liberation Day annually on 10 May.
The date commemorates the island’s liberation in 1945 from German occupation during the Second World War.
St Helena’s national day commemorates the island’s discovery in 1502 by Galician navigator João da Nova, then serving the King of Portugal.
Anchoring in the present James Bay, da Nova named the island ‘Santa Helena’ after St Helena of Constantinople, whose feast according to the Orthodox Church falls on 21 May.
Anguilla Day takes place annually on 30 May.
On 30 May 1967 the Anguillans began a revolution that led to independence from the union of St Kitts-Nevis-Anguilla.
Bermuda Day first took place as Empire Day on 24 May 1902.
It continued on that day until 2018, when it moved to the last Friday of May.
It is also known as Heritage Day, celebrating the island’s culture and heritage.
The Falkland Islands celebrate Liberation Day annually on 14 June.
The date commemorates the liberation of the islands from Argentine military occupation in 1982.