Sir - you cannot buy a shotgun of modern manufacture, even a muzzleloader that uses loose powder, without a SGC.
You CAN buy a smoothbored antique firearm without any form of licence, except a birth certificate that shows that you are over 18 yo, even a rifled frearm that is an antique of an obslolete calibre, but you are not permitted to shoot it unless you subsequently license it either as a shotgun - smoothbore and SGC, or Section 1 firearm - rifled.
tac