The search did not reveal a specific current event for why UK flags are at half-mast today, September 17, 2025. Typically, in the UK, flags are flown at half-mast as a mark of respect, mourning, or distress under certain official circumstances. These include:

• From the announcement of the death until the funeral of the sovereign or members of the royal family.
• Funerals of foreign rulers, prime ministers, or ex-prime ministers, upon command of the sovereign.
• Other occasions by special command of the sovereign.

If there is a specific event today requiring flags at half-mast, it is likely related to an official period of mourning or commemoration ordered by the government or monarchy.

Since no specific news source indicates a recent death or official event for today, it might be worth checking local or governmental announcements for special commemorations or mourning orders specific to this date. If more precise data is needed, a follow-up check on recent news for the UK could be performed. Would you like me to do that?