Europe Day is celebrated annually on 5 May and 9 May.
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
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
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/
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
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.
Somerset Day was selected by public vote from a shortlist that includes: 19 May – Feast of St Dunstan; 6 July – Battle of Sedgemoor.
The battle of Albuera (1811) took place during the Peninsular War, when Anglo-Portuguese forces defeated the French.
The 57th (West Middlesex) Foot suffered very heavy casualties during the battle and later celebrated the anniversary as a regimental day.
The International Day against Homophobia, Transphobia and Biphobia 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 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.
St Aldhelm (639–709) was Abbot of Malmesbury and Bishop of Sherborne.
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.