If you read the Firearms act it actually doesn’t mention pistols of handguns, save in the context of “air pistols”.
Otherwise it talks about Firearms. It does define a “shotgun” as have a smooth bore of greater than 24” and if it has a magazine, then it can only contain no more than two cartridges, and the magazine must be fixed to the gun and the ammunition must contain at least 5 shot each of no more than .36” in diameter.
Section 5 prohibits
any firearm which either has a barrel less than 30 centimetres in length or is less than 60 centimetres in length overall, other than an air weapon,
F21. . . a muzzle-loading gun or a firearm designed as signalling apparatus;
S5 also prohibits self loading or pump action guns other than a smooth bore shotgun of at least 40” long, or a rifle chambered for a 22 rimfire cartridge.
This effectively prohibits the general use and ownership under section 1 of cartridge firing handguns.
There is no mention of different types of section 1 firearms. Section 1 covers any firearm that is not either a shotgun, an air weapon (under 12 ft lbs or 6 ft lbs in case of a pistol) or a covered by section 5 prohibition.
There is no mention in the Firearms Act of long barrelled pistols. A Smith & Wesson with a butt extension and a 30cm barrel and total length of 60cm could be described as a short revolver rifle or a revolver carbine.
For that matter something like a short barreled Bergara B13 is the same length as a LBP and can be just as easily fired single handed like a pistol. Or fir that matter so could a very short chassis and pistol grip bolt action rifle.
Somehow, as in all things firearms there is a whole other layer of bs added over and above what is necessary.