"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.
"He had never counted on anything except surprise and unpredictability and danger" from Lee Child's Bad Luck and Trouble novel (2007)---------------
"There's always the chance I'll screw up. That's what keeps it from getting boring."
from Dean Koontz's The Eyes of Darkness novel (1981)