A conjugate of formula: wherein: R 2 is where R 36a and R 36b are independently selected from H, F, C 1-4 saturated alkyl, C 2-3 alkenyl, which alkyl and alkenyl groups are optionally substituted by a group selected from C 1-4 alkyl amido and C 1-4 alkyl ester; or, when one of R 36a and R 36b is H, the other is selected from nitrile and a C 1-4 alkyl ester; R 6 and R 9 are independently selected from H, R, OH, OR, SH, SR, NH 2, NHR, NRR', NO 2, Me 3 Sn and halo; R 7 is independently selected from H, R, OH, OR, SH, SR, NH 2, NHR, NRR', NO 2, Me 3 Sn and halo; Y is selected from formulae A1, A2, A3, A4, A5 and A6: L is a linker connected to a cell binding agent; CBA is the cell binding agent; n is an integer selected in the range of 0 to 48; R A4 is a C 1-6 alkylene group; either (a) R 10 is H, and R 11 is OH, OR A, where R A is C 1-4 alkyl; or (b) R 10 and R 11 form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound; or (c) R 10 is H and R 11 is OSO z M, where z is 2 or 3 and M is a monovalent pharmaceutically acceptable cation; R and R' are each independently selected from optionally substituted C 1-12 alkyl, C 3-20 heterocyclyl and C 5-20 aryl groups, and optionally in relation to the group NRR', R and R' together with the nitrogen atom to which they are attached form an optionally substituted 4-, 5-, 6- or 7-membered heterocyclic ring; wherein R 16, R 17, R 19, R 20, R 21 and R 22 are as defined for R 6, R 7, R 9, R 10, R 11 and R 2 respectively; wherein Z is CH or N; wherein T and T' are independently selected from a single bond or a C 1-9 alkylene, which chain may be interrupted by one or more heteroatoms e.g. O, S, N, NMe, provided that the number of atoms in the shortest chain of atoms between X and X' is 3 to 12 atoms; and X and X' are independently selected from O, S and N. R 2 is where R 36a and R 36b are independently selected from H, F, C 1-4 saturated alkyl, C 2-3 alkenyl, which alkyl and alkenyl groups are optionally substituted by a group selected from C 1-4 alkyl amido and C 1-4 alkyl ester; or, when one of R 36a and R 36b is H, the other is selected from nitrile and a C 1-4 alkyl ester; R 6 and R 9 are independently selected from H, R, OH, OR, SH, SR, NH 2, NHR, NRR', NO 2, Me 3 Sn and halo; R 7 is independently selected from H, R, OH, OR, SH, SR, NH 2, NHR, NRR', NO 2, Me 3 Sn and halo; Y is selected from formulae A1, A2, A3, A4, A5 and A6: L is a linker connected to a cell binding agent; CBA is the cell binding agent; n is an integer selected in the range of 0 to 48; R A4 is a C 1-6 alkylene group; either (a) R 10 is H, and R 11 is OH, OR A, where R A is C 1-4 alkyl; or (b) R 10 and R 11 form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound; or (c) R 10 is H and R 11 is OSO z M, where z is 2 or 3 and M is a monovalent pharmaceutically acceptable cation; (a) R 10 is H, and R 11 is OH, OR A, where R A is C 1-4 alkyl; or (b) R 10 and R 11 form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound; or (c) R 10 is H and R 11 is OSO z M, where z is 2 or 3 and M is a monovalent pharmaceutically acceptable cation; R and R' are each independently selected from optionally substituted C 1-12 alkyl, C 3-20 heterocyclyl and C 5-20 aryl groups, and optionally in relation to the group NRR', R and R' together with the nitrogen atom to which they are attached form an optionally substituted 4-, 5-, 6- or 7-membered heterocyclic ring; wherein R 16, R 17, R 19, R 20, R 21 and R 22 are as defined for R 6, R 7, R 9, R 10, R 11 and R 2 respectively; wherein Z is CH or N; wherein T and T' are independently selected from a single bond or a C 1-9 alkylene, which chain may be interrupted by one or more heteroatoms e.g. O, S, N, NMe, provided that the number of atoms in the shortest chain of atoms between X and X' is 3 to 12 atoms; and X and X' are independently selected from O, S and N.