"The 33 bhp category disappears in the EU from January as more age related restrictions come in, but there will now be a 47 bhp intermediate licence category."
The Harley 883cc Sportster and the 400cc Ninja have about 45 peak horsepower- maybe the UK rule makers looked at these 2 bikes.
My Honda 600cc cruiser has about 33 peak horsepower with a custom exhaust and rejetting, giving it about the same top speed as a 250cc Ninja, but it is slower in corners because it weighs more and scrapes the footpegs sooner, with its lower seat and frame.
"We have created a Star Wars civilization, with Stone Age emotions, medieval institutions, and godlike technology. We thrash about. We are terribly confused by the mere fact of our existence, and a danger to ourselves and to the rest of life.”
― from Edward O. Wilson, The Social Conquest of Earth.