A compound of formula (Ia) or a pharmaceutically acceptable salt thereof wherein W1, X1, Y1 and Z1 each independently represent N, NH or CH, wherein at least two of W1, X1, Y1 and Z1 represent N or NH ； p is 0, 1, 2 or 3； each R11 independently represents halogen, cyano, C1-C6 alkoxy, C1-C6 haloalkyl, C1-C6 haloalkoxy, C1-C6 alkylthio, (C1-C6 alkyl) -carbonyl, or C1-C6 alkyl optionally substituted with carboxyl or (C1 alkoxy -C6) -carbonyl； q is 0, 1, 2, 3 or 4； each R12 independently represents halogen, cyano, carboxyl, hydroxyl, C1-C6 alkyl, C1-C6 haloalkyl, C1-C6 alkoxy, C1-C6 hydroxyalkyl, (C1-C6 alkoxy) -carbonyl, (C1-C6 alkoxy) - (alkyl C1-C6) or a 5- to 9-membered heterocyclic ring system； R13 represents an oxygen atom or a group C>； = O, NR15 or CR16R17, with the proviso that (i) when R13 represents CO or NH and ring A represents pyrazol-4-yl or imidazol-4-yl, then p must be 3 and R14 represents a substituted phenyl, pyridinyl or naphthyl ring system, and (ii) when R13 represents CH2 and ring A represents pyrazol-4-yl or imidazol-4-yl, then either p is 3 , or, p is 2 and q is at least 1； R15 represents a hydrogen atom or a C1-C6 alkyl group； R16 and R17 each independently represent a hydrogen or halogen or cyano atom, carboxyl, hydroxyl, C1-C6 alkyl, C1-C6 haloalkyl, C1-C6 alkoxy, C1-C6 hydroxyalkyl, (C1-C6 alkoxy) -carbonyl, ( C1-C6 alkoxy) - (C1-C6 alkyl) or a 5- to 9-membered heterocyclic ring system； R14 represents a phenyl, pyridinyl or naphthyl ring system, the ring system itself being optionally substituted with at least one substituent selected from halogen, hydroxyl, cyano, oxo, C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl , C1-C6 haloalkyl, C1-C6 hydroxyalkyl, C1-C6 alkoxy, C1-C6 haloalkoxy, C1-C6 alkylthio, C1-C6 alkylsulfinyl, C1-C6 alkylsulfonyl, (C1-C6 alkyl) -carbonyl, (C1-C6 alkyl ) -carbonyloxy, (C1-C6 alkoxy) -carbonyl, amino, -CON (R18) 2, (C1-C6 alkyl) amino, di- (C1-C6 alkyl) amino, C3-C6 cycloalkyl, C3-C6 cycloalkyloxy or (C3-C6 cycloalk
