I honestly can’t tell if Glupton’s trolling…
To do the manoeuvre properly you go into the gap smoothly with an early indicator then once your settled in the gap you gently decrease your speed to take the gap back to a safe one.
So, the gap’s not safe (“take the gap back to a safe one”) and to make it safe you’re relying on forcing another driver to slow down and create space, which besides being specifically against the Highway Code is downright inconsiderate to other road users, and dependant on other drivers reacting how you expect them to… And you’re doing this because…
That’s not a maneuvre that most drivers “don’t know about”, it’s a maneuvre that most people just choose not to use.