In this case I believe Wikipedia is correct:
Long-barrelled revolvers and pistols
"Long-barrelled revolvers" and "long-barrelled pistols" meeting specified criteria are not classified as prohibited pistols; it is legal, with a Class I Firearms Certificate, to own them. The barrel must be at least 30 cm long, and the firearm at least 60 cm long, which can be achieved by having a permanently attached extension to the grip or butt of the firearm. Single-shot firearms of any calibre, and
semi-automatic pistols of .22 rimfire calibres, are permitted.
They are certainly not Section 5.