A gas turbine engine comprising: a compressor section having a downstream rotor and a diffuser downstream of said compressor section; a combustor, said combustor for receiving air downstream of the diffuser a combustor housing being positioned downstream of an outlet of said diffuser; a turbine section having at least one component to be cooled; and a cooling airflow conduit spaced from said diffuser and defining a cooling airflow path (198;288), said cooling airflow path (198;288) being separate from an airflow path downstream said diffuser, and passing to said combustor, with said conduit passing cooling air to said component to be cooled, wherein said cooling airflow path (189;288) is tapped from a location downstream of a compressor vane which is downstream of said downstream rotor, and upstream of said diffuser; wherein said conduit is provided by a pair of radially spaced shells (90,92; 190,192;290,292), wherein said shells (90,92; 190; 192) extend for 360° about a center axis of the engine and are positioned radially inwardly of said diffuser and said combustor; characterised in that: the combustor housing is positioned such that air downstream of said diffuser bends through an approximately ninety degree angle in one radial direction, flows axially along an outer surface of the housing then moves back through an approximately ninety degree angle into a combustion chamber through inlet ports; and wherein shells (290;292) are also positioned radially outwardly of said diffuser and said combustor section to provide a second cooling airflow path. a compressor section having a downstream rotor and a diffuser downstream of said compressor section; a combustor, said combustor for receiving air downstream of the diffuser a combustor housing being positioned downstream of an outlet of said diffuser; a turbine section having at least one component to be cooled; and a cooling airflow conduit spaced from said diffuser and defining a cooling airflow path (198;288), said cooling airflow path (198;288) being separate from an airflow path downstream said diffuser, and passing to said combustor, with said conduit passing cooling air to said component to be cooled, wherein said cooling airflow path (189;288) is tapped from a location downstream of a compressor vane which is downstream of said downstream rotor, and upstream of said diffuser; wherein said conduit is provided by a pair of radially spaced shells (90,92; 190,192;290,292), wherein said shells (90,92; 190; 192) extend for 360° about a center axis of the engine and are positioned radially inwardly of said diffuser and said combustor; characterised in that: the combustor housing is positioned such that air downstream of said diffuser bends through an approximately ninety degree angle in one radial direction, flows axially along an outer surface of the housing then moves back through an approximately ninety degree angle into a combustion chamber through inlet ports; and wherein shells (290;292) are also positioned radially outwardly of said diffuser and said combustor section to provide a second cooling airflow path. the combustor housing is positioned such that air downstream of said diffuser bends through an approximately ninety degree angle in one radial direction, flows axially along an outer surface of the housing then moves back through an approximately ninety degree angle into a combustion chamber through inlet ports; and wherein shells (290;292) are also positioned radially outwardly of said diffuser and said combustor section to provide a second cooling airflow path.