I also found the brake eff test a bit odd (at least in terms of numbers). Percent of what?
I asked the MoT bloke and he said it was something to do with % of weight vs braking effort or something. Minimum to pass was only 25% IIRC.
Apparently 100% would pretty much mean your brakes would lock the wheel instantly (which wouldn't be great!)
Can't remember what my numbers were now, but the tester was suitably impressed. He also used the rolling road device.

Google turned up this:
"Motorcycles first registered on or after 1 January 1927 require two means of operating the brakes, one achieving a minimum efficiency of 30% and the other a minimum of 25%."

"Calculate the service brake percentage efficiency by dividing the total brake effort achieved when the service brake is applied by the vehicle weight and then multiply the result by 100."

Real women don't have the surname ".JPG"