The pilot undergoing the check flight had completed a helicopter instructor course about two months earlier and had not flown this helicopter type for nine years. He was being checked for future employment as a Grade 2 helicopter instructor. The early part of the flight was conducted in the training area where various types of circuit and approaches were carried out satisfactorily. On return to the aerodrome the instructor demonstrated an autorotation to touchdown. The pilot under check then conducted two autorotations to touchdown. The instructor reported that during the touchdown phase on the second landing the other pilot applied excessive collective control. He attempted to correct the situation but was physically unable to prevent the other pilot from raising the control. Rotor rpm decayed excessively and the tail boom was severed in the ensuing hard landing. The pilot under check was experienced on another type of helicopter requiring a different landing technique from this one. He was also not used to having another pilot making control inputs and did not give precedence to these inputs. The instructor had evidently made no verbal comment to the other pilot that he was applying corrective inputs to the controls.