A compound of formula wherein R 1 represents an 8- to 10-membered fused bicyclic heteroaromatic group optionally substituted by at least one substituent selected from halogen, cyano, hydroxyl, C 3 -C 6 cycloalkyl, C 1 -C 3 alkyl, C 1 -C 3 alkoxy, C 1 -C 3 alkoxycarbonyl, C 1 -C 3 alkoxycarbonylamino, C 1 -C 3 haloalkoxy, -NR 4 R 5, C 3 -C 6 cycloalkylamino, C 1 -C 3 alkylcarbonyloxy, C 1 -C 3 alkylcarbonylamino, sulphonamido, C 1 -C 3 alkylsulphonyl, C 1 -C 3 alkylsulphonylamino and -C NR 6 R 7; L represents CH 2, O, NH or N(CH 3); R a represents a hydrogen atom or a C 1 -C 3 alkyl or C 1 -C 3 haloalkyl group; R b represents a hydrogen atom or a C 1 -C 3 alkyl or C 1 -C 3 haloalkyl group; X represents CF 2, CHR 8 O or NC R 9; R 2 represents a hydrogen atom or a C 1 -C 6 alkyl group; n is 0 or an integer 1, 2, 3, 4 or 5; each R 3 independently represents halogen, hydroxyl, cyano, C 1 -C 3 alkyl, C 1 -C 3 haloalkyl, C 1 -C 3 hydroxyalkyl, C 1 -C 3 alkoxy, C 1 -C 3 haloalkoxy, C 2 -C 4 alkenyl, C 1 -C 3 alkylcarbonyloxy, C 1 -C 3 alkoxycarbonyl, -NR 10 R 11, -CONR 12 R 13, C 3 -C 6 cycloalkyl, C 3 -C 6 cycloalkyloxy, C 3 -C 6 cycloalkylmethyl or a 5- to 6-membered heteroaryl group, the heteroaryl group being optionally substituted by at least one substituent selected from C 1 -C 6 alkyl, C 1 -C 6 alkoxy and C 1 -C 6 haloalkoxy; R 4 and R 5 each independently represent a hydrogen atom or a C 1 -C 3 alkyl or C 3 -C 6 cycloalkyl group, or R 4 and R 5 may together with the nitrogen atom to which they are attached form a 4- to 7-membered saturated heterocyclic ring optionally substituted by at least one substituent selected from halogen and hydroxyl; R 6 and R 7 each independently represent a hydrogen atom or a C 1 -C 3 alkyl or C 3 -C 6 cycloalkyl group, or R 6 and R 7 may together with the nitrogen atom to which they are attached form a 4- to 7-membered saturated heterocyclic ring optionally substituted by at least one substituent selected from halogen and hydroxyl; R 8 represents a hydrogen or halogen atom or a hydroxyl group; R 9 represents a C 1 -C 6 alkyl, C 1 -C 6 alkoxy, benzyloxy, C 6 -C 10 aryl, or heteroaryl group; R 10 and R 11 each independently represent a hydrogen atom or a C 1 -C 3 alkyl or C 3 -C 6 cycloalkyl group, or R 10 and R 11 may together with the nitrogen atom to which they are attached form a 4- to 7-membered saturated heterocyclic ring optionally substituted by at least one substituent selected from halogen and hydroxyl; and R 12 and R 13 each independently represent a hydrogen atom or a C 1 -C 3 alkyl or C 3 -C 6 cycloalkyl group, or R 12 and R 13 may together with the nitrogen atom to which they are attached form a 4- to 7-membered saturated heterocyclic ring optionally substituted by at least one substituent selected from halogen and hydroxyl; or a pharmaceutically acceptable salt thereof. R 1 represents an 8- to 10-membered fused bicyclic heteroaromatic group optionally substituted by at least one substituent selected from halogen, cyano, hydroxyl, C 3 -C 6 cycloalkyl, C 1 -C 3 alkyl, C 1 -C 3 alkoxy, C 1 -C 3 alkoxycarbonyl, C 1 -C 3 alkoxycarbonylamino, C 1 -C 3 haloalkoxy, -NR 4 R 5, C 3 -C 6 cycloalkylamino, C 1 -C 3 alkylcarbonyloxy, C 1 -C 3 alkylcarbonylamino, sulphonamido, C 1 -C 3 alkylsulphonyl, C 1 -C 3 alkylsulphonylamino and -C NR 6 R 7; L represents CH 2, O, NH or N(CH 3); R a represents a hydrogen atom or a C 1 -C 3 alkyl or C 1 -C 3 haloalkyl group; R b represents a hydrogen atom or a C 1 -C 3 alkyl or C 1 -C 3 haloalkyl group; X represents CF 2, CHR 8 O or NC R 9; R 2 represents a hydrogen atom or a C 1 -C 6 alkyl group; n is 0 or an integer 1, 2, 3, 4 or 5; each R 3 independently represents halogen, hydroxyl, cyano, C 1 -C 3 alkyl, C 1 -C 3 haloalkyl, C 1 -C 3 hydroxyalkyl, C 1 -C 3 alkoxy, C 1 -C 3 haloalkoxy, C 2 -C 4 alkenyl, C 1 -C 3 alkylcarbonyloxy, C 1 -C 3 alkoxycarbonyl, -NR 10 R 11, -CONR 12 R 13, C 3 -C 6 cycloalkyl, C 3 -C 6 cycloalkyloxy, C 3 -C 6 cycloalkylmethyl or a 5- to 6-membered heteroaryl group, the heteroaryl group being optionally substituted by at least one substituent selected from C 1 -C 6 alkyl, C 1 -C 6 alkoxy and C 1 -C 6 haloalkoxy; R 4 and R 5 each independently represent a hydrogen atom or a C 1 -C 3 alkyl or C 3 -C 6 cycloalkyl group, or R 4 and R 5 may together with the nitrogen atom to which they are attached form a 4- to 7-membered saturated heterocyclic ring optionally substituted by at least one substituent selected from halogen and hydroxyl; R 6 and R 7 each independently represent a hydrogen atom or a C 1 -C 3 alkyl or C 3 -C 6 cycloalkyl group, or R 6 and R 7 may together with the nitrogen atom to which they are attached form a 4- to 7-membered saturated heterocyclic ring optionally substituted by at least one substituent selected from halogen and hydroxyl; R 8 represents a hydrogen or halogen atom or a hydroxyl group; R 9 represents a C 1 -C 6 alkyl, C 1 -C 6 alkoxy, benzyloxy, C 6 -C 10 aryl, or heteroaryl group; R 10 and R 11 each independently represent a hydrogen atom or a C 1 -C 3 alkyl or C 3 -C 6 cycloalkyl group, or R 10 and R 11 may together with the nitrogen atom to which they are attached form a 4- to 7-membered saturated heterocyclic ring optionally substituted by at least one substituent selected from halogen and hydroxyl; and R 12 and R 13 each independently represent a hydrogen atom or a C 1 -C 3 alkyl or C 3 -C 6 cycloalkyl group, or R 12 and R 13 may together with the nitrogen atom to which they are attached form a 4- to 7-membered saturated heterocyclic ring optionally substituted by at least one substituent selected from halogen and hydroxyl;