A valve actuation mechanism comprises a housing, an actuation pin rotatably mounted within the housing and at least one torque spring coupling the actuation pin to the housing for biasing the actuation pin from a first, inoperative rotational position towards a second, operative rotational position. The mechanism further comprises an actuation pin retaining element for selectively retaining the actuation pin in its first position, the retaining element being engageable with the actuation pin and the housing when the retaining element is in a retaining position so as to prevent rotation of the actuation pin towards its second position, and selectively disengageable from the housing to permit rotation of the actuation pin towards its second position. A locking element is provided for selectively preventing disengagement of the retaining element from the housing.