A compound of the formula: or a salt thereof, wherein: p is 0, 1 or 2; V is a bond, Q 1 is nitrogen and Q 2 is nitrogen or carbon; or V is selected from NH, N(C 1-3 alkyl), NH-CH 2 and N(C 1-3 alkyl)-CH 2 and Q 1 and Q 2 each represent carbon; W is -Q 3 C YCH 2 R 4 or optionally substituted 1-oxa-2,4-diazole, wherein when W is 1-oxa-2,4-diazole, Q 2 is carbon; Q 3 is a bond or a group -(Alk) q -NR 6 where Alk is an alkyl group of 1 to 4 carbon atoms; q is 0 or 1; and R 6 is hydrogen or a saturated C 1-4 hydrocarbon group; provided that when Q 2 is nitrogen and Q 3 is a group -(Alk) q -NR 6, there are at least two carbon atoms in line between Q 2 and NR 6 and provided that when Q 3 is a bond, Q 2 is nitrogen; X 1 and X 2 are optionally substituted saturated hydrocarbon groups which together contain a total of one to nine carbon atoms and which link together such that the moiety: forms a monocyclic or bicyclic ring system; Q 4 is an optionally substituted five or six membered aromatic carbocyclic or heterocyclic group containing 0, 1, 2 or 3 heteroatom ring members selected from O, N and S, wherein Q 4 is unsubstituted or is substituted with one or more substituents Q 6 selected from halogen; cyano; hydroxy; amino; and a C 1-10 non-aromatic hydrocarbon group which is optionally substituted with one to six fluorine atoms and wherein one, two or three, but not all, carbon atoms of the hydrocarbon group may optionally be replaced by a heteroatom selected from O, N and S and oxidized forms thereof; or Q 4 forms an optionally substituted heterocyclic spirocyclic ring with Q 5; Q 5 is selected from hydrogen; fluorine; cyano; hydroxy; amino; and a C 1-9 non-aromatic hydrocarbon group which is optionally substituted with one to six fluorine atoms and wherein one, two or three, but not all, carbon atoms of the hydrocarbon group may optionally be replaced by a heteroatom selected from O, N and S and oxidized forms thereof, or forms an optionally substituted heterocyclic spirocyclic ring with Q 4; Y is CH or O; R 4 is hydrogen or a C 1-6 non-aromatic hydrocarbon group which is optionally substituted with one to six fluorine atoms and wherein one or two, but not all, carbon atoms of the hydrocarbon group may optionally be replaced by a heteroatom selected from O, N and S and oxidised forms thereof; and R 5 is fluorine or a C 1-4 hydrocarbon group p is 0, 1 or 2; V is a bond, Q 1 is nitrogen and Q 2 is nitrogen or carbon; or V is selected from NH, N(C 1-3 alkyl), NH-CH 2 and N(C 1-3 alkyl)-CH 2 and Q 1 and Q 2 each represent carbon; W is -Q 3 C YCH 2 R 4 or optionally substituted 1-oxa-2,4-diazole, wherein when W is 1-oxa-2,4-diazole, Q 2 is carbon; Q 3 is a bond or a group -(Alk) q -NR 6 where Alk is an alkyl group of 1 to 4 carbon atoms; q is 0 or 1; and R 6 is hydrogen or a saturated C 1-4 hydrocarbon group; provided that when Q 2 is nitrogen and Q 3 is a group -(Alk) q -NR 6, there are at least two carbon atoms in line between Q 2 and NR 6 and provided that when Q 3 is a bond, Q 2 is nitrogen; X 1 and X 2 are optionally substituted saturated hydrocarbon groups which together contain a total of one to nine carbon atoms and which link together such that the moiety: forms a monocyclic or bicyclic ring system; Q 4 is an optionally substituted five or six membered aromatic carbocyclic or heterocyclic group containing 0, 1, 2 or 3 heteroatom ring members selected from O, N and S, wherein Q 4 is unsubstituted or is substituted with one or more substituents Q 6 selected from halogen; cyano; hydroxy; amino; and a C 1-10 non-aromatic hydrocarbon group which is optionally substituted with one to six fluorine atoms and wherein one, two or three, but not all, carbon atoms of the hydrocarbon group may optionally be replaced by a heteroatom selected from O, N and S and oxidized forms thereof; or Q 4 forms an optionally substituted heterocyclic spirocyclic ring with Q 5; Q 5 is selected from hydrogen; fluorine; cyano; hydroxy; amino; and a C 1-9 non-aromatic hydrocarbon group which is optionally substituted with one to six fluorine atoms and wherein one, two or three, but not all, carbon atoms of the hydrocarbon group may optionally be replaced by a heteroatom selected from O, N and S and oxidized forms thereof, or forms an optionally substituted heterocyclic spirocyclic ring with Q 4; Y is CH or O; R 4 is hydrogen or a C 1-6 non-aromatic hydrocarbon group which is optionally substituted with one to six fluorine atoms and wherein one or two, but not all, carbon atoms of the hydrocarbon group may optionally be replaced by a heteroatom selected from O, N and S and oxidised forms thereof; and R 5 is fluorine or a C 1-4 hydrocarbon group