A detainer disc locking system comprising: a key; a lock housing including a face plate with a keyhole for receiving the key and a first side bar channel formed in the lock housing; a lock cylinder disposed within the lock housing so as to be selectively rotatable relative to the lock housing, the lock cylinder including a second side bar channel formed in the lock cylinder; a side bar at least partially received within the second side bar channel and being movable between a first position in which the side bar traverses a shear plane between the lock cylinder and the lock housing such that the lock cylinder is fixed relative to the lock housing and a second position in which a shear plane between the lock housing and the lock cylinder is uninterrupted by the side bar so as to enable rotation of the lock cylinder relative to the lock housing; an idler block disposed within the lock cylinder, the idler block including a key channel receiving the key therein such that the idler block is rotatable with the key relative to the lock cylinder; and a plurality of detainer discs disposed within the lock cylinder, each detainer disc being annular in shape and being supported about the idler block so as to be rotatable relative to the lock cylinder, and each detainer disc further comprising (i) a gate channel formed at an outer edge of the detainer disc such that the detainer disc blocks movement of the side bar into the second position until the gate channel is aligned with the second side bar channel and (ii) a key bit formed at an inner edge of the detainer disc; the idler block at least partially blocking access to the detainer discs; the key including a plurality of keyed surfaces forming a key profile of the key, each keyed surface being aligned with a respective one of the detainer discs such that rotation of the key relative to the lock housing in an unlocking direction towards an unlocking orientation of the key causes the keyed surfaces of the key to engage the key bits of the detainer discs respectively so as to align the gate channels of the detainer discs with the second side bar channel in the lock housing. a key; a lock housing including a face plate with a keyhole for receiving the key and a first side bar channel formed in the lock housing; a lock cylinder disposed within the lock housing so as to be selectively rotatable relative to the lock housing, the lock cylinder including a second side bar channel formed in the lock cylinder; a side bar at least partially received within the second side bar channel and being movable between a first position in which the side bar traverses a shear plane between the lock cylinder and the lock housing such that the lock cylinder is fixed relative to the lock housing and a second position in which a shear plane between the lock housing and the lock cylinder is uninterrupted by the side bar so as to enable rotation of the lock cylinder relative to the lock housing; an idler block disposed within the lock cylinder, the idler block including a key channel receiving the key therein such that the idler block is rotatable with the key relative to the lock cylinder; and a plurality of detainer discs disposed within the lock cylinder, each detainer disc being annular in shape and being supported about the idler block so as to be rotatable relative to the lock cylinder, and each detainer disc further comprising (i) a gate channel formed at an outer edge of the detainer disc such that the detainer disc blocks movement of the side bar into the second position until the gate channel is aligned with the second side bar channel and (ii) a key bit formed at an inner edge of the detainer disc; the idler block at least partially blocking access to the detainer discs; the key including a plurality of keyed surfaces forming a key profile of the key, each keyed surface being aligned with a respective one of the detainer discs such that rotation of the key relative to the lock housing in an unlocking direction towards an unlocking orientation of the key causes the keyed surfaces of the key to engage the key bits of the detainer discs respectively so as to align the gate channels of the detainer discs with the second side bar channel in the lock housing.