“Such sudden huge surges in demand tied to the TV schedule are unique to the United Kingdom.”

Why? (The text source doesn’t make this claim.)

Jump down to the Cause section. Millions of high-powered electric kettles being switched on during a popular show's break.

But why is that unique to the UK? Plenty of other cultures use electric kettles and follow soaps. (Also did streaming dent the effect?)

You vastly underestimate the consumption of tea in the United Kingdom. It's funny that America is almost the only country that does plug-in drip coffeemakers, though, since most people that follow "their shows" in the United States probably would be much less likely to trip a circuit suddenly.

1. it is a cultural thing, many are doing it 2. they have very powerful kettles

Do they still occur now that nobody is watching linear TV?

Yes. There are still large culturally significant events, such as the World Cup, that enough people gather around over to be of note.

Further linked within was an old BBC article; http://news.bbc.co.uk/2/hi/uk_news/magazine/6981356.stm

"... there aren't very many examples of sudden decreases in demand triggered by TV programmes. A rare example would be the two minutes' silence at 11am on Remembrance Sunday, but this occurs during daylight hours so is nowhere near comparable."

I'm remembering when the Queen passed now - it was very interesting to see a lot of systems at some major retailers lose their minds because of a super sharp order volume drop from normal expectations. It fired off all sorts of automations to investigate service outages... only for a few tickets a few minutes later to pop in to announce the death of the Queen and how to work that onto the homepage.