Using handbrake in cornering slows the car down. To push a 131 through a corner you need to brake hard with foot, turn the steering one way and quickly the other way. Put the pedal down and the rear end does the rest. That's the way to do so with a rear wheel driven car.
It's just that a handbrake is needed for MOT, otherwise i would leave it.
Sorry, but I disagree with a thrust of your comment.
You are - in principle - correct as far as the technique goes but ...
Any time you use a brake it slows the car down. This is what breaking is all about (almost). "Almost", because braking also serves to transfer the weight to front wheels (to increase traction) as well as to position the car in the curve itself (typically just about the middle of the curve). BTW: braking in the curve is a no no on a civilian car not prepared for rallies).
The handbrake is however used to loose traction on rear wheels , where you do not have enough space to perform normal left-right-left-right sequence ( or when the traction on the rear wheels to too big to swing it sideways when you need it.
Vary useful as you can make a quicker turn when the curve is somewhere between 300 to 360 degrees.( "swipe" with your rear end - so to speak).
Also , applying brakes ( both by foot as well as by a hand) does not mean you have to take off your foot of the accelerator...
Nevertheless this kind of advance driving technique is not a natural driver's behavior. Be warned: do not try it on a open road, and train a lot (on closed roads only !) to muster it , before you start using it. It takes years of practice to do it safely and instinctively.
Remember it was developed by people like Rauno Aaltonen, who said that he trains all day at least 100 days a year (by trying all day to set a Mini Cooper on the roof).
Miro