A compound of formula, wherein: R represents hydrogen or halo; R 3 represents hydrogen, hydroxy, halo, cyano, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy, C 1-4 hydroxyalkyl, C 1-4 haloalkoxy, -O(CH 2) 2 OH or -O(CH 2) 2 OC 1-2 alkyl; R 4 represents hydrogen, halo, cyano, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy or C 1-4 haloalkoxy; R 5 represents hydrogen, halo, cyano, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy or C 1-4 haloalkoxy; m and n represent integers which may be independently selected from 1 and 2; and either (a) R 1 represents hydrogen, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy, C 1-2 alkoxyC 1-2 alkyl or C 1-4 haloalkoxy; and R 2 represents hydrogen, halo, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy, C 1-4 haloalkoxy, C 1-2 alkoxyC 1-2 alkyl, C 1-4 hydroxyalkyl or cyano; or (b) R 1 and R 2 are in positions 6 and 5 respectively of the pyridine nucleus and are joined to form a bicyclic system comprising either a 5- or 6-membered carbocyclic ring or a 5- or 6-membered heterocyclic ring which contains heteroatoms selected only from O and S, which is fused to said pyridine nucleus; or a pharmaceutically acceptable salt thereof. R represents hydrogen or halo; R 3 represents hydrogen, hydroxy, halo, cyano, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy, C 1-4 hydroxyalkyl, C 1-4 haloalkoxy, -O(CH 2) 2 OH or -O(CH 2) 2 OC 1-2 alkyl; R 4 represents hydrogen, halo, cyano, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy or C 1-4 haloalkoxy; R 5 represents hydrogen, halo, cyano, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy or C 1-4 haloalkoxy; m and n represent integers which may be independently selected from 1 and 2; and either (a) R 1 represents hydrogen, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy, C 1-2 alkoxyC 1-2 alkyl or C 1-4 haloalkoxy; and R 2 represents hydrogen, halo, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy, C 1-4 haloalkoxy, C 1-2 alkoxyC 1-2 alkyl, C 1-4 hydroxyalkyl or cyano; or (b) R 1 and R 2 are in positions 6 and 5 respectively of the pyridine nucleus and are joined to form a bicyclic system comprising either a 5- or 6-membered carbocyclic ring or a 5- or 6-membered heterocyclic ring which contains heteroatoms selected only from O and S, which is fused to said pyridine nucleus; (a) R 1 represents hydrogen, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy, C 1-2 alkoxyC 1-2 alkyl or C 1-4 haloalkoxy; and R 2 represents hydrogen, halo, C 1-4 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C 1-4 alkoxy, C 1-4 haloalkoxy, C 1-2 alkoxyC 1-2 alkyl, C 1-4 hydroxyalkyl or cyano; or (b) R 1 and R 2 are in positions 6 and 5 respectively of the pyridine nucleus and are joined to form a bicyclic system comprising either a 5- or 6-membered carbocyclic ring or a 5- or 6-membered heterocyclic ring which contains heteroatoms selected only from O and S, which is fused to said pyridine nucleus; or a pharmaceutically acceptable salt thereof.