A sealing device, comprising: a metal seal, the metal seal having a generally I-shaped cross section, the metal seal including arms (30a,30b,40a,40b) extending axially outward from a radially extending central web thereby defining opposed first and second recesses (42a,42b) between the arms (30a,40a and 30b,40b), each arm (30a,30b,40a,40b) comprising a sealing surface such that the metal seal comprises first, second, third and fourth sealing surfaces (32a,32b,38), the first metal sealing surface (32a,32b) forming a metal to metal seal with the internal cylindrical sealing surface, and the second metal sealing surface forming a metal to metal seal with the external cylindrical sealing surface, the sealing device further including a first non-metal seal disposed in a first recess in the metal seal, the first recess positioned radially between the first and second metal sealing surfaces (32a,32b,38), the first nonmetal seal biasing the first metal sealing surface (32a,32b) against the internal cylindrical sealing surface and biases the second metal sealing surface against the external cylindrical sealing surface in response to a first pressure differential across the sealing device, the sealing device further including a second non-metal seal disposed in a second recess in the metal seal, the second recess positioned between third and fourth metal sealing surfaces (32a,32b,38), the second nonmetal seal biasing the third metal sealing surface (32a,32b) against the internal cylindrical sealing surface and biases the fourth metal sealing surface against the external cylindrical sealing surface in response to a second pressure differential across the sealing device, the second pressure differential being in an opposite direction to the first pressure differential, the first and second nonmetal seals (48a,48b) include nonmetal sealing surfaces (50,52) in contact with the internal and external cylindrical sealing surfaces (44,46), and characterised in that the first nonmetal seal includes a third recess which axially overlaps at least a portion of the first recess and the second nonmetal seal includes a fourth recess which axially overlaps at least a portion of the second recess. a metal seal, the metal seal having a generally I-shaped cross section, the metal seal including arms (30a,30b,40a,40b) extending axially outward from a radially extending central web thereby defining opposed first and second recesses (42a,42b) between the arms (30a,40a and 30b,40b), each arm (30a,30b,40a,40b) comprising a sealing surface such that the metal seal comprises first, second, third and fourth sealing surfaces (32a,32b,38), the first metal sealing surface (32a,32b) forming a metal to metal seal with the internal cylindrical sealing surface, and the second metal sealing surface forming a metal to metal seal with the external cylindrical sealing surface, the sealing device further including a first non-metal seal disposed in a first recess in the metal seal, the first recess positioned radially between the first and second metal sealing surfaces (32a,32b,38), the first nonmetal seal biasing the first metal sealing surface (32a,32b) against the internal cylindrical sealing surface and biases the second metal sealing surface against the external cylindrical sealing surface in response to a first pressure differential across the sealing device, the sealing device further including a second non-metal seal disposed in a second recess in the metal seal, the second recess positioned between third and fourth metal sealing surfaces (32a,32b,38), the second nonmetal seal biasing the third metal sealing surface (32a,32b) against the internal cylindrical sealing surface and biases the fourth metal sealing surface against the external cylindrical sealing surface in response to a second pressure differential across the sealing device, the second pressure differential being in an opposite direction to the first pressure differential, the first and second nonmetal seals (48a,48b) include nonmetal sealing surfaces (50,52) in contact with the internal and external cylindrical sealing surfaces (44,46), and characterised in that the first nonmetal seal includes a third recess which axially overlaps at least a portion of the first recess and the second nonmetal seal includes a fourth recess which axially overlaps at least a portion of the second recess.