A turbine comprising: a turbine housing defining a turbine inlet upstream of a turbine wheel and a turbine outlet downstream of the turbine wheel; a wastegate passage connecting the turbine inlet and the turbine outlet; a wastegate valve comprising a movable valve member; the wastegate valve having an open state in which gas may pass between the turbine inlet and turbine outlet via the wastegate passage and a closed state in which the valve member substantially prevents gas from passing between the turbine inlet and the turbine outlet via the wastegate passage; wherein the wastegate valve further comprises a valve seat, the valve member contacting the valve seat when the wastegate valve is in the closed state; and wherein the valve member is mounted to an actuation member having a longitudinal axis, the actuation member passing through an actuator conduit of the turbine housing, and being movable so as to move the wastegate valve between the open and closed states; the turbine further comprising a sealing arrangement configured to provide a seal arranged to substantially prevent gas from passing from the turbine outlet into the actuator conduit; characterized in that the valve seat is angled relative to the longitudinal axis and is configured such that when the actuation member urges the valve member of the wastegate valve into the closed state, the valve seat imparts a force on the valve member which urges the valve member in a first substantially axial direction; and, wherein the sealing arrangement is configured such that the urging of the valve member in the first substantially axial direction increases the sealing effectiveness of the sealing arrangement. a turbine housing defining a turbine inlet upstream of a turbine wheel and a turbine outlet downstream of the turbine wheel; a wastegate passage connecting the turbine inlet and the turbine outlet; a wastegate valve comprising a movable valve member; the wastegate valve having an open state in which gas may pass between the turbine inlet and turbine outlet via the wastegate passage and a closed state in which the valve member substantially prevents gas from passing between the turbine inlet and the turbine outlet via the wastegate passage; wherein the wastegate valve further comprises a valve seat, the valve member contacting the valve seat when the wastegate valve is in the closed state; and wherein the valve member is mounted to an actuation member having a longitudinal axis, the actuation member passing through an actuator conduit of the turbine housing, and being movable so as to move the wastegate valve between the open and closed states; the turbine further comprising a sealing arrangement configured to provide a seal arranged to substantially prevent gas from passing from the turbine outlet into the actuator conduit; characterized in that the valve seat is angled relative to the longitudinal axis and is configured such that when the actuation member urges the valve member of the wastegate valve into the closed state, the valve seat imparts a force on the valve member which urges the valve member in a first substantially axial direction; and, wherein the sealing arrangement is configured such that the urging of the valve member in the first substantially axial direction increases the sealing effectiveness of the sealing arrangement.