MJ
I suspect CGB is referring to the aircraft performance safety factors from CAA Safety Sense leaflets (and other places). This recommends a 1.43 multiplier as a final safety factor (if aircraft flight manual data is unfactored) for landing distance.
Although it may not be entirely to compensate for pilots who can't maintain the correct approach speed/technique. It could also allow some margin for changes in temperature, wind, surface wetness from those used for the pre departure calculations.