Yeah we all know its significance in the US. Because US movies and media are a huge export.

It is just not considered significant when making any plans.

In the UK the whole US UK war was the act of a mad King. Our parliment at the time refused to fund it. And the war bankrupted the royal family. Sorta leading to our current odd funding. Where parliment profits from royal land. And funds the monarch in exchange.

So the events have more historical significance then average brits recognise. But we don’t tend to treat the date any differently beyond the odd. “Oh the yanks will be on holiday.”