A compound of formula or a pharmaceutically acceptable salt thereof, wherein in formula W, X, Y and Z each independently represent N, NH or CH, with the proviso that W, X, Y and Z do not each simultaneously represent a moiety CH; m is 0, 1, 2 or 3; each R 1 independently represents halogen, cyano, C 1 -C 6 alkoxy, C 3 -C 6 cycloalkyl, C 1 -C 6 alkoxycarbonyl, C 1 -C 6 haloalkyl, C 1 -C 6 haloalkoxy, C 1 -C 6 alkylthio, C 1 -C 6 alkylcarbonyl, or C 1 -C 6 alkyl optionally substituted by carboxyl or C 1 -C 6 alkoxycarbonyl; n is 0, 1, 2, 3 or 4; each R 2 independently represents halogen, cyano, carboxyl, hydroxyl, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 1 -C 6 alkoxy, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxycarbonyl, C 1 -C 6 alkoxyC 1 -C 6 alkyl or a 5- to 9-membered heterocyclic ring system; R 3 represents =CR 6, or, when there is at least one R 1 group present that represents a C 3 -C 6 cycloalkyl group, then R 3 may additionally represent a group -CR 7 R 8 -; R 5 is absent or represents a hydrogen atom or a substituent as defined above for R 2; R 6 represents a hydrogen or halogen atom or a cyano, C 1 -C 6 alkyl or C 1 -C 6 alkoxycarbonyl group; R 7 and R 8 each independently represent a hydrogen or halogen atom or cyano, carboxyl, hydroxyl, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 1 -C 6 alkoxy, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxycarbonyl, C 1 -C 6 alkoxyC 1 -C 6 alkyl or a 5- to 9-membered heterocyclic ring system; R 4 represents a 6- to 10-membered aromatic or heteroaromatic ring system, the ring system itself being optionally substituted by at least one substituent selected from halogen, hydroxyl, cyano, oxo, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 1 -C 6 haloalkyl, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxy, C 1 -C 6 haloalkoxy, C 1 -C 6 alkylthio, C 1 -C 6 alkylsulphinyl, C 1 -C 6 alkylsulphonyl, C 1 -C 6 alkylcarbonyl, C 1 -C 6 alkylcarbonyloxy, C 1 -C 6 alkoxycarbonyl, amino, -CON(R 9) 2, C 1 -C 6 alkylamino, di-(C 1 -C 6 alkyl)amino, C 3 -C 6 cycloalkyl, C 3 -C 6 cycloalkyloxy or C 3 -C 6 cycloalkylmethyl; and each R 9 independently represents a hydrogen atom or a C 1 -C 6 alkyl group; provided that the compound of formula is not: 1-[(1-methyl-1H-pyrazol-4-yl)sulfonyl]-4-(phenylmethylene)piperidine; 1-[[1-cyclopentyl-3-(1,1-dimethylethyl)-1H-pyrazol-4-yl]sulfonyl]-4-(phenylmethyl)piperidine; 1-[(1-cyclopentyl-3-methyl-1H-pyrazol-4-yl)sulfonyl]-4-(phenylmethyl)piperidine; 1-[(5-chloro-1-methyl-1H-imidazol-4-yl)sulfonyl]-4-[(3-fluorophenyl)-methylene]piperidine; or 4-(1-(4-chlorophenyl)ethylidene)-1-((3,5-dimethyl-1H-pyrazol-4-yl)sulfonyl)piperidine. W, X, Y and Z each independently represent N, NH or CH, with the proviso that W, X, Y and Z do not each simultaneously represent a moiety CH; m is 0, 1, 2 or 3; each R 1 independently represents halogen, cyano, C 1 -C 6 alkoxy, C 3 -C 6 cycloalkyl, C 1 -C 6 alkoxycarbonyl, C 1 -C 6 haloalkyl, C 1 -C 6 haloalkoxy, C 1 -C 6 alkylthio, C 1 -C 6 alkylcarbonyl, or C 1 -C 6 alkyl optionally substituted by carboxyl or C 1 -C 6 alkoxycarbonyl; n is 0, 1, 2, 3 or 4; each R 2 independently represents halogen, cyano, carboxyl, hydroxyl, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 1 -C 6 alkoxy, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxycarbonyl, C 1 -C 6 alkoxyC 1 -C 6 alkyl or a 5- to 9-membered heterocyclic ring system; R 3 represents =CR 6, or, when there is at least one R 1 group present that represents a C 3 -C 6 cycloalkyl group, then R 3 may additionally represent a group -CR 7 R 8 -; R 5 is absent or represents a hydrogen atom or a substituent as defined above for R 2; R 6 represents a hydrogen or halogen atom or a cyano, C 1 -C 6 alkyl or C 1 -C 6 alkoxycarbonyl group; R 7 and R 8 each independently represent a hydrogen or halogen atom or cyano, carboxyl, hydroxyl, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 1 -C 6 alkoxy, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxycarbonyl, C 1 -C 6 alkoxyC 1 -C 6 alkyl or a 5- to 9-membered heterocyclic ring system; R 4 represents a 6- to 10-membered aromatic or heteroaromatic ring system, the ring system itself being optionally substituted by at least one substituent selected from halogen, hydroxyl, cyano, oxo, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 1 -C 6 haloalkyl, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxy, C 1 -C 6 haloalkoxy, C 1 -C 6 alkylthio, C 1 -C 6 alkylsulphinyl, C 1 -C 6 alkylsulphonyl, C 1 -C 6 alkylcarbonyl, C 1 -C 6 alkylcarbonyloxy, C 1 -C 6 alkoxycarbonyl, amino, -CON(R 9) 2, C 1 -C 6 alkylamino, di-(C 1 -C 6 alkyl)amino, C 3 -C 6 cycloalkyl, C 3 -C 6 cycloalkyloxy or C 3 -C 6 cycloalkylmethyl; and each R 9 independently represents a hydrogen atom or a C 1 -C 6 alkyl group; 1-[(1-methyl-1H-pyrazol-4-yl)sulfonyl]-4-(phenylmethylene)piperidine; 1-[[1-cyclopentyl-3-(1,1-dimethylethyl)-1H-pyrazol-4-yl]sulfonyl]-4-(phenylmethyl)piperidine; 1-[(1-cyclopentyl-3-methyl-1H-pyrazol-4-yl)sulfonyl]-4-(phenylmethyl)piperidine; 1-[(5-chloro-1-methyl-1H-imidazol-4-yl)sulfonyl]-4-[(3-fluorophenyl)-methylene]piperidine; or 4-(1-(4-chlorophenyl)ethylidene)-1-((3,5-dimethyl-1H-pyrazol-4-yl)sulfonyl)piperidine.