An exhaust system for an internal combustion engine, which system comprising: a) a first catalysed substrate monolith comprising: a first washcoat coating disposed in a first washcoat zone of the substrate monolith, wherein the first washcoat coating comprises a catalyst composition comprising at least one platinum group metal and at least one support material, wherein the at least one platinum group metal in the first washcoat coating comprises platinum, which is liable to volatilise when the first washcoat coating is exposed to relatively extreme conditions including relatively high temperatures of ≥ 700°C; a second washcoat coating disposed in a second washcoat zone of the substrate monolith, wherein the second washcoat coating comprises at least one support material supporting copper for trapping volatilised platinum group metal, wherein the at least one support material is at least one metal oxide, a molecular sieve or a mixture of any two or more thereof, and wherein when the at least one support material is at least one metal oxide then the at least one metal oxide support is selected from the group consisting of optionally stabilised alumina, amorphous silica-alumina, optionally stabilised zirconia, titania, an optionally stabilised ceria-zirconia mixed oxide and a mixture of any two or more thereof, and wherein the second washcoat coating is oriented to contact exhaust gas that has contacted the first washcoat; and b) a second catalysed substrate monolith comprising a catalyst for selectively catalysing the reduction of oxides of nitrogen to dinitrogen with a nitrogenous reductant disposed downstream from the first catalysed substrate monolith. a) a first catalysed substrate monolith comprising: a first washcoat coating disposed in a first washcoat zone of the substrate monolith, wherein the first washcoat coating comprises a catalyst composition comprising at least one platinum group metal and at least one support material, wherein the at least one platinum group metal in the first washcoat coating comprises platinum, which is liable to volatilise when the first washcoat coating is exposed to relatively extreme conditions including relatively high temperatures of ≥ 700°C; a second washcoat coating disposed in a second washcoat zone of the substrate monolith, wherein the second washcoat coating comprises at least one support material supporting copper for trapping volatilised platinum group metal, wherein the at least one support material is at least one metal oxide, a molecular sieve or a mixture of any two or more thereof, and wherein when the at least one support material is at least one metal oxide then the at least one metal oxide support is selected from the group consisting of optionally stabilised alumina, amorphous silica-alumina, optionally stabilised zirconia, titania, an optionally stabilised ceria-zirconia mixed oxide and a mixture of any two or more thereof, and wherein the second washcoat coating is oriented to contact exhaust gas that has contacted the first washcoat; and a first washcoat coating disposed in a first washcoat zone of the substrate monolith, wherein the first washcoat coating comprises a catalyst composition comprising at least one platinum group metal and at least one support material, wherein the at least one platinum group metal in the first washcoat coating comprises platinum, which is liable to volatilise when the first washcoat coating is exposed to relatively extreme conditions including relatively high temperatures of ≥ 700°C; a second washcoat coating disposed in a second washcoat zone of the substrate monolith, wherein the second washcoat coating comprises at least one support material supporting copper for trapping volatilised platinum group metal, wherein the at least one support material is at least one metal oxide, a molecular sieve or a mixture of any two or more thereof, and wherein when the at least one support material is at least one metal oxide then the at least one metal oxide support is selected from the group consisting of optionally stabilised alumina, amorphous silica-alumina, optionally stabilised zirconia, titania, an optionally stabilised ceria-zirconia mixed oxide and a mixture of any two or more thereof, and wherein the second washcoat coating is oriented to contact exhaust gas that has contacted the first washcoat; and b) a second catalysed substrate monolith comprising a catalyst for selectively catalysing the reduction of oxides of nitrogen to dinitrogen with a nitrogenous reductant disposed downstream from the first catalysed substrate monolith.