A rotor for a steam turbine, comprising: a high pressure turbine rotor section (16,210) having a first end and a second end; and an intermediate pressure turbine rotor section (18,212) joined to the second end of the high pressure turbine rotor section; wherein the high pressure turbine rotor section (16,210) comprises: a high temperature material section formed of a high temperature material, and having a first end and a second end opposite thereof; a first low temperature material section formed of a first low temperature material, the first low temperature material section joined to the first end of the high temperature material section and extending from the first end of the high temperature material section towards the first end of the high pressure turbine rotor section; characterised in that the high pressure turbine rotor section further comprises: a second low temperature material section formed of a second low temperature material, the second low temperature material section joined to the second end of the high temperature material and extending from the second end of the high temperature material section towards the second end of the high pressure turbine rotor section, wherein the second end of the high temperature material section is provided upstream of a first turbine stage of the high pressure turbine section, the first low temperature section at least partially extending downstream of a last turbine stage of the high pressure turbine section, and the shaft high temperature material section being formed of a single unitary section or block of high temperature material. a high pressure turbine rotor section (16,210) having a first end and a second end; and an intermediate pressure turbine rotor section (18,212) joined to the second end of the high pressure turbine rotor section; wherein the high pressure turbine rotor section (16,210) comprises: a high temperature material section formed of a high temperature material, and having a first end and a second end opposite thereof; a first low temperature material section formed of a first low temperature material, the first low temperature material section joined to the first end of the high temperature material section and extending from the first end of the high temperature material section towards the first end of the high pressure turbine rotor section; characterised in that the high pressure turbine rotor section further comprises: a second low temperature material section formed of a second low temperature material, the second low temperature material section joined to the second end of the high temperature material and extending from the second end of the high temperature material section towards the second end of the high pressure turbine rotor section, wherein the second end of the high temperature material section is provided upstream of a first turbine stage of the high pressure turbine section, the first low temperature section at least partially extending downstream of a last turbine stage of the high pressure turbine section, and the shaft high temperature material section being formed of a single unitary section or block of high temperature material. a high temperature material section formed of a high temperature material, and having a first end and a second end opposite thereof; a first low temperature material section formed of a first low temperature material, the first low temperature material section joined to the first end of the high temperature material section and extending from the first end of the high temperature material section towards the first end of the high pressure turbine rotor section; characterised in that the high pressure turbine rotor section further comprises: a second low temperature material section formed of a second low temperature material, the second low temperature material section joined to the second end of the high temperature material and extending from the second end of the high temperature material section towards the second end of the high pressure turbine rotor section, wherein the second end of the high temperature material section is provided upstream of a first turbine stage of the high pressure turbine section, the first low temperature section at least partially extending downstream of a last turbine stage of the high pressure turbine section, and the shaft high temperature material section being formed of a single unitary section or block of high temperature material. a second low temperature material section formed of a second low temperature material, the second low temperature material section joined to the second end of the high temperature material and extending from the second end of the high temperature material section towards the second end of the high pressure turbine rotor section, wherein the second end of the high temperature material section is provided upstream of a first turbine stage of the high pressure turbine section, the first low temperature section at least partially extending downstream of a last turbine stage of the high pressure turbine section, and the shaft high temperature material section being formed of a single unitary section or block of high temperature material.