A compound of formula or a pharmaceutically acceptable salt thereof: wherein one of X and Y is N and the other is C; L is a linker group selected from -(CH 2) a -Q-(CH 2) b - in which, Q is selected from the group comprising: O, NH, SO 2, C=C, and C=C or Q is absent; R 1 is selected from a ring: in which: (a) all of T, V, W and Z are C, or (b) T is C and one or two of V, W and Z is N and the remainder of them is/are C, or (c) T is absent, and one of V, W and Z is C and the other two are N; or R 1 is a mono- or bicyclic ring substituted by one R 3 group and 0, 1, or 2 R 4 groups; R 2 is -C OH, -C OM or wherein M is a group 1 cation; R 3 is either absent or is selected as appropriate to satisfy valence requirements from the group comprising: H, halo, CN, oxo, C 1-6 alkyl, C 1-6 alkoxy, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, -(CH 2) d -aryl, -(CH 2) d -heteroaryl, -(CH 2) e -heterocyclyl, -OR 5, -N(R 5) 2, -SO 2 R 5, - SO 2 N(R 5) 2, -NHSO 2 R 7, -NHCOR 5, -CON(R 5) 2 and -COR 5 wherein each of the above substituents apart from H may themselves be optionally substituted where chemically possible with one, two or three groups independently selected at each occurrence from the group comprising: halo, -N(R 5) 2, -OH, -C(=O)C 1-6 alkyl, -SO 2 N(C 1-6 alkyl) 2, -(CH 2) h OR 5, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, and C 3-8 cycloalkenyl; R 4 and R 5 are independently selected at each occurrence from the group comprising: H, halo, -OH, C 1-6 alkyl, C 1-6 haloalkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, C 3-8 cycloalkenyl, -(CH 2) f -aryl, -(CH 2) d -heteroaryl, -(CH 2) g -heterocyclyl; wherein each of R 4 and R 5 may themselves be optionally substituted where chemically possible with one, two or three groups independently selected at each occurrence from the group comprising: halo, -NH 2, -N(C 1-4 alkyl) 2, -OH, -SO 2 N(C 1-4 alkyl) 2, -NHC(=O)OC 1-6 alkyl, and -C(=O)OC 1-6 alkyl; R 6 is selected from the group comprising: H, C 1-4 alkyl, and C 1-4 haloalkyl; R 7 is selected from the group comprising: H, C 1-4 alkyl, C 1-4 haloalkyl, C 1-4 alkyl amine, C 3-8 cycloalkyl and aryl, and 5 to 10 membered heteroaryl; a, b, d, e, f, g and h are independently selected as integers from 0 to 3; and n is an integer selected from:0 to 2; and - - - represents a single or a double bond as required to satisfy valence requirements. one of X and Y is N and the other is C; L is a linker group selected from -(CH 2) a -Q-(CH 2) b - in which, Q is selected from the group comprising: O, NH, SO 2, C=C, and C=C or Q is absent; R 1 is selected from a ring: in which: (a) all of T, V, W and Z are C, or (b) T is C and one or two of V, W and Z is N and the remainder of them is/are C, or (c) T is absent, and one of V, W and Z is C and the other two are N; or R 1 is a mono- or bicyclic ring substituted by one R 3 group and 0, 1, or 2 R 4 groups; R 2 is -C OH, -C OM or wherein M is a group 1 cation; R 3 is either absent or is selected as appropriate to satisfy valence requirements from the group comprising: H, halo, CN, oxo, C 1-6 alkyl, C 1-6 alkoxy, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, -(CH 2) d -aryl, -(CH 2) d -heteroaryl, -(CH 2) e -heterocyclyl, -OR 5, -N(R 5) 2, -SO 2 R 5, - SO 2 N(R 5) 2, -NHSO 2 R 7, -NHCOR 5, -CON(R 5) 2 and -COR 5 wherein each of the above substituents apart from H may themselves be optionally substituted where chemically possible with one, two or three groups independently selected at each occurrence from the group comprising: halo, -N(R 5) 2, -OH, -C(=O)C 1-6 alkyl, -SO 2 N(C 1-6 alkyl) 2, -(CH 2) h OR 5, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, and C 3-8 cycloalkenyl; R 4 and R 5 are independently selected at each occurrence from the group comprising: H, halo, -OH, C 1-6 alkyl, C 1-6 haloalkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, C 3-8 cycloalkenyl, -(CH 2) f -aryl, -(CH 2) d -heteroaryl, -(CH 2) g -heterocyclyl; wherein each of R 4 and R 5 may themselves be optionally substituted where chemically possible with one, two or three groups independently selected at each occurrence from the group comprising: halo, -NH 2, -N(C 1-4 alkyl) 2, -OH, -SO 2 N(C 1-4 alkyl) 2, -NHC(=O)OC 1-6 alkyl, and -C(=O)OC 1-6 alkyl; R 6 is selected from the group comprising: H, C 1-4 alkyl, and C 1-4 haloalkyl; R 7 is selected from the group comprising: H, C 1-4 alkyl, C 1-4 haloalkyl, C 1-4 alkyl amine, C 3-8 cycloalkyl and aryl, and 5 to 10 membered heteroaryl; a, b, d, e, f, g and h are independently selected as integers from 0 to 3; and n is an integer selected from:0 to 2; and - - - represents a single or a double bond as required to satisfy valence requirements.