A pressure reducing valve comprising: a supporting element that is slidable relative to a sealing element, the sealing element incorporating a sealing part for sealing a valve seat; a regulator biasing member; and an actuating mechanism (905, 1001) that is operable to apply an actuating force to the supporting element to move it towards the valve seat, the actuating force being adjustable through a threshold value, the valve being configured such that: the supporting element is pressed by secondary pressure towards the valve seat and by the regulator biasing member away from the valve seat; further characterised in that the sealing element is biased by a closing biasing member towards the valve seat, the closing biasing member being fixed to the supporting element, and the supporting element includes a stop to arrest movement of the sealing element towards the valve seat; wherein: the closing biasing member and threshold value of the actuating force are configured such that a load applied to the supporting element by the closing biasing member is: sufficient to ensure that the sealing element rests on the stop if the actuating force is less than the threshold value, thereby ensuring that the sealing and supporting elements are moveable as a single unit under the influence of the regulator biasing member, secondary pressure and any sub-threshold actuating force; and set such that on application of an actuating force equal to the threshold value, the sealing element is moved relative to the supporting element such that it no longer rests on the stop, thereby ensuring that the sealing part is pressed onto the valve seat predominantly under the influence of the closing biasing member. a supporting element that is slidable relative to a sealing element, the sealing element incorporating a sealing part for sealing a valve seat; a regulator biasing member; and an actuating mechanism (905, 1001) that is operable to apply an actuating force to the supporting element to move it towards the valve seat, the actuating force being adjustable through a threshold value, the valve being configured such that: the supporting element is pressed by secondary pressure towards the valve seat and by the regulator biasing member away from the valve seat; further characterised in that the sealing element is biased by a closing biasing member towards the valve seat, the closing biasing member being fixed to the supporting element, and the supporting element includes a stop to arrest movement of the sealing element towards the valve seat; wherein: the closing biasing member and threshold value of the actuating force are configured such that a load applied to the supporting element by the closing biasing member is: sufficient to ensure that the sealing element rests on the stop if the actuating force is less than the threshold value, thereby ensuring that the sealing and supporting elements are moveable as a single unit under the influence of the regulator biasing member, secondary pressure and any sub-threshold actuating force; and set such that on application of an actuating force equal to the threshold value, the sealing element is moved relative to the supporting element such that it no longer rests on the stop, thereby ensuring that the sealing part is pressed onto the valve seat predominantly under the influence of the closing biasing member. the supporting element is pressed by secondary pressure towards the valve seat and by the regulator biasing member away from the valve seat; further characterised in that the sealing element is biased by a closing biasing member towards the valve seat, the closing biasing member being fixed to the supporting element, and the supporting element includes a stop to arrest movement of the sealing element towards the valve seat; wherein: the closing biasing member and threshold value of the actuating force are configured such that a load applied to the supporting element by the closing biasing member is: sufficient to ensure that the sealing element rests on the stop if the actuating force is less than the threshold value, thereby ensuring that the sealing and supporting elements are moveable as a single unit under the influence of the regulator biasing member, secondary pressure and any sub-threshold actuating force; and set such that on application of an actuating force equal to the threshold value, the sealing element is moved relative to the supporting element such that it no longer rests on the stop, thereby ensuring that the sealing part is pressed onto the valve seat predominantly under the influence of the closing biasing member. sufficient to ensure that the sealing element rests on the stop if the actuating force is less than the threshold value, thereby ensuring that the sealing and supporting elements are moveable as a single unit under the influence of the regulator biasing member, secondary pressure and any sub-threshold actuating force; and set such that on application of an actuating force equal to the threshold value, the sealing element is moved relative to the supporting element such that it no longer rests on the stop, thereby ensuring that the sealing part is pressed onto the valve seat predominantly under the influence of the closing biasing member.